Google Adsense ads are not natively responsive but there are some simple solutions that can help you optimise ad sizes for different devices.
Responsive Ads Solutions
Click Missile Ads Plugin
In a Nutshell:
Making your ads mobile responsive with Click Missile
When you create a mobile sized ad with Click Missile tick the is this ad for mobile devices box.
Then when you make a Click Missile ad widget the mobile ad will be available for selection in the Ad to display on mobile devices drop down box.
Now whenever the plugin detects that your site is being viewed on a mobile phone, it will automatically show a mobile ad.
The great thing about the Click Missile solution is that its easy and there’s no need to mess about with Google Adsense code. Just paste and go.
Click Missile plugin is very handy to have when you use this technique as it allows you to easily create ad widgets containing the code and place them on your site. Most importantly it allows you to switch off desktop and tablet sized ads, and switch to mobile sized ads placed in positions which are more suitable for mobile phones.
You can also embed responsive Adsense code into HeatMap AdAptive ad widgets.
For more information about this technique read our post Responsive Google Adsense Ads for WordPress.