Kostoski started his pro career with French team Pau Orthez in 2004.

Kostoski has also been a member of the Macedonian national basketball team since 2004, when he represented Macedonia at the FIBA Europe Under-16 Championship.

[3] Aleksandar Kostoski was a candidate for the Macedonian national basketball team for the 2012 FIBA World Olympic Qualifying Tournament in Caracas, Venezuela.

[4] According to the Coach Marjan Lazovski, Kostoski, along with Kiril Nikolovski and Bojan Trajkovski are likely to be the newest additions to the final team.

[5] On 29 August 2018 he signed with Macedonian basketball club Gostivar.