Since 2017 28 year-old Kostov is a member of the Liberic Theatre in the Czech Republic, where he can be seen in numerous roles:
as SINODAL in Rubenstein’s “Demon” von Rubinstein, YOUNG GIPSY in «Aleko», NEMORINO in “L'elisir d'amore”, RINUCCIO in “Gianni Schicchi”, LENSKY in “Eugen Onegin”, BORSA and DUKA in “Rigoletto”, RAIMUND in Tschaikowski’s “The Maid of Orleans”, ISMAILE and ABDALLO in “Nabucco”, TONIK in Smetana’s “Dvě vdovy”, the PRINCE in “Rusalka”, PAOLO in “Francesca di Rimini” and ALBERT in Rachmaninoff’s “The Miserly Knight”, DON OTTAVIO in “Don Giovanni”, NADIR in “Die Perlenfischer”.

In summer 2021 he made his debut as GORO in „Madama Buttefly“ and in gala concerts at the Chiemgau Festival Gut Immling.

"Sergej Kostov is plays a wonderfully slimy matchmaker Goro with an exceptionally beautiful tenor timbre." Iris Steiner wrote in the opera magazine Orpheus.

In summer 2022 he returned to Immling and sang here once again GORO as well as FLAVIO in “Norma” and several concerts. In the season 2022/23 Sergej makes his debut at the Neustrelitz Theatre as MONSIEUR TRIQUET in Tschaikowski’ s “Eugen Onegin” – a production that was just postponed because of the COVID 19 pandemic.

The son of Bulgarian parents started his musical studies at the Odessa Music College. He made his Bachelor and Master of Music at the Odessa National A.V. Nezhdanova Academy of Music.

In 2014 he won the 1st Prize at the International Vocal Forum in Italy and in 2017 the 2nd Prize at the International Singing Competition VISSI D’ARTE in Prague.

First stage experiences he made in Odessa.
From 2014 to 2017 he performed with the Ukrainian Military Orchestra in Ukraine in Odessa.
From 2011 to 2017 he was a concert soloist at the Orthodox Preobrazhenskiy Cathedral in Odessa. At the same time he was soloist of the "Svitoch National Orchestra.

In 2018 he had a guest performance as FÜRST STERNENHOCH in der opera „Sternenhoch“ at the der Prague National Opera.