<form action="">

<select required>

  <option selected disabled value="">choose</option>
  <option value="red">red</option>
  <option value="yellow">yellow</option>
  <option value="green">green</option>
  <option value="grey">grey</option>

</select>
<input type="submit">
</form>

<select>元素支持required属性，按照规范:

http://dev.w3.org/html5/spec-author-view/the-select-element.html#the-select-element

哪个浏览器不支持这个功能?

(当然，无论如何您都必须在服务器上验证，因为您不能保证用户将启用JavaScript。)

首先，您必须在第一个选项中分配空白值。 选择这里。而不是只需要工作。

试试这个

<select>
<option value="" style="display:none">Please select</option>
<option value="one">One</option>
</select>

<form action="">

<select required>

  <option selected disabled value="">choose</option>
  <option value="red">red</option>
  <option value="yellow">yellow</option>
  <option value="green">green</option>
  <option value="grey">grey</option>

</select>
<input type="submit">
</form>

Works perfectly fine if the first option's value is null. Explanation : The HTML5 will read a null value on button submit. If not null (value attribute), the selected value is assumed not to be null hence the validation would have worked i.e by checking if there's been data in the option tag. Therefore it will not produce the validation method. However, i guess the other side becomes clear, if the value attribute is set to null ie (value = "" ), HTML5 will detect an empty value on the first or rather the default selected option thus giving out the validation message. Thanks for asking. Happy to help. Glad to know if i did.