Sebastian Michał Chmara (Polish pronunciation: [sɛˈbastjan ˈmixaw ˈxmara]; born 21 November 1971) is a former decathlete from Poland who became world indoor champion in 1999 and European indoor champion in 1998 (both in heptathlon, as decathlon is unsuitable for indoor contests).

His personal bests are 8566 points in the decathlon (Alhama de Murcia 1998) and 6415 points in the indoor heptathlon (Valencia 1998).

Both are standing national records.

He is a cousin of a former pole vaulter, Mirosław Chmara.

This biographical article relating to Polish athletics is a stub.