Starting May 18th, Cartoon Network's anime night will add the straw hat pirates at 1:00 AM on it's Saturday (technically Sunday) Toonami block. One Piece has not been featured on Cartoon Network in any form in quite some years, and will air relatively uncensored as compared to it's past morning/afternoon heavily censored airings on the Cartoon Network of past.
Cartoon Network's Toonami seems to be going back to basics as it has also started to once again play Naruto recently, which will be the show immediately airing before One Piece on Saturday (or again technically Sunday) nights.
The show will of course be in it's English language dubbed format.
Some rumors also indicate dubbed versions of Eureka 7 AO and Inuyasha Final Act may be on the way for Toonami as well, but those rumors are presently just that, rumors.
One Piece will replace the sadly cancelled ThunderCats series in the Toonami line-up.