The 25-year-old Macedonia international tested positive for steroid stanozolol after Dinamo's 2-1 Champions League win over Arsenal in September 2015.
European football's governing body Uefa gave him a four-year ban, which its appeals panel upheld last May.
But Cas, on appeal, found a reduction to two years was appropriate.
Ademi had asked for the ban to be overturned completely, but Cas said "it could not uphold the player's argument that the challenged decision should be annulled".
He will now be eligible for club and country from October.
Dinamo Zagreb midfielder Arijan Ademi's four-year doping ban has been halved as the Court of Arbitration for Sport found he did not intentionally cheat.