diff --git a/src/generate-axios-client.test.ts b/src/generate-axios-client.test.ts
index 67f9df7..0c893f7 100644
--- a/src/generate-axios-client.test.ts
+++ b/src/generate-axios-client.test.ts
@@ -68,12 +68,16 @@ const substituteParams = (url, params) =>
     url
   );
 
-const removePathParams = (url, params) =>
-  Object.entries(params).reduce(
-    (accum, [name, value]) =>
-      url.includes(":" + name) ? accum : { ...accum, [name]: value },
-    {}
-  );
+const removePathParams = (url, params, encode) =>
+  Object.entries(params)
+    .filter(([key, value]) => value !== undefined)
+    .reduce(
+      (accum, [name, value]) =>
+        url.includes(":" + name)
+          ? accum
+          : { ...accum, [name]: encode ? encodeURIComponent(value) : value },
+      {}
+    );
 
 const parseQueryParamsFromPagingLink = (link) => {
   const params = new URLSearchParams(link.split("?")[1]);
@@ -89,12 +93,12 @@ class Client {
     this.client = client;
   }
 
-  getPosts(params, config) {
+  getPosts(data, config) {
     return this.client.request({
       ...config,
       method: "GET",
-      params: removePathParams("/posts", params),
-      url: substituteParams("/posts", params),
+      params: removePathParams("/posts", data, true),
+      url: substituteParams("/posts", data),
     });
   }
 
@@ -102,7 +106,7 @@ class Client {
     return this.client.request({
       ...config,
       method: "PUT",
-      data: removePathParams("/posts/:id", data),
+      data: removePathParams("/posts/:id", data, false),
       url: substituteParams("/posts/:id", data),
     });
   }
diff --git a/src/generate-axios-client.ts b/src/generate-axios-client.ts
index af49182..63ac518 100644
--- a/src/generate-axios-client.ts
+++ b/src/generate-axios-client.ts
@@ -64,12 +64,16 @@ const substituteParams = (url, params) =>
     url
   );
 
-const removePathParams = (url, params) => 
-  Object.entries(params).reduce(
-    (accum, [name, value]) =>
-      url.includes(':' + name) ? accum : { ...accum, [name]: value },
-    {}
-  );
+const removePathParams = (url, params, encode) => 
+  Object.entries(params)
+    .filter(([key, value]) => value !== undefined)
+    .reduce(
+      (accum, [name, value]) =>
+        url.includes(':' + name)
+          ? accum
+          : { ...accum, [name]: encode ? encodeURIComponent(value) : value },
+      {}
+    );
 
 const parseQueryParamsFromPagingLink = (link) => {
   const params = new URLSearchParams(link.split('?')[1]);
@@ -89,15 +93,18 @@ class ${outputClass} {
   ${Object.entries(spec.Endpoints)
     .map(([endpoint, { Name }]) => {
       const [method, url] = endpoint.split(' ');
-      const paramsName = method === 'GET' ? 'params' : 'data';
-
+      const useQueryParams = ['GET', 'DELETE'].includes(method);
       return `
-        ${Name}(${paramsName}, config) {
+        ${Name}(data, config) {
           return this.client.request({
             ...config,
             method: '${method}',
-            ${paramsName}: removePathParams('${url}', ${paramsName}),
-            url: substituteParams('${url}', ${paramsName}),
+            ${
+              useQueryParams
+                ? `params: removePathParams('${url}', data, true),`
+                : `data: removePathParams('${url}', data, false),`
+            }
+            url: substituteParams('${url}', data),
           })
         }
       `;
diff --git a/src/integration.axios.test.ts b/src/integration.axios.test.ts
index 186d650..6b387dc 100644
--- a/src/integration.axios.test.ts
+++ b/src/integration.axios.test.ts
@@ -143,6 +143,34 @@ describe('integration tests', () => {
     });
   });
 
+  test('generated code URI-encodes query parameters', async () => {
+    const { client, request } = await prepare();
+
+    await client.listPosts({ filter: 'some/evil/string' });
+
+    expect(request).toHaveBeenCalledTimes(1);
+    expect(request).toHaveBeenCalledWith({
+      method: 'GET',
+      url: '/posts/list',
+      params: {
+        filter: 'some%2Fevil%2Fstring',
+      },
+    });
+  });
+
+  test('generated code does not send undefined query parameters', async () => {
+    const { client, request } = await prepare();
+
+    await client.listPosts({ filter: undefined });
+
+    expect(request).toHaveBeenCalledTimes(1);
+    expect(request).toHaveBeenCalledWith({
+      method: 'GET',
+      url: '/posts/list',
+      params: {},
+    });
+  });
+
   test('pagination', async () => {
     const { client, request } = await prepare();