From Test-Scratch-Wiki
Scratch 2.0 can be used on mobile devices if they have Adobe Flash Player. Otherwise, there is a app called Scratch Jr that can be used on mobile devices but is very different to Scratch. Even if you don't have flash player, you can still post in the forums and view and comment on projects, you just aren't able to run or edit projects.
It is possible that in a future update, such as 3.0, Scratch can be used on mobile devices without the need of Flash.
