Denis Istomin (born September 7, 1986 in Tashkent, Uzbek SSR, USSR) is an Uzbekistani professional tennis player. His career high rank is #57, achieved on July 27, 2009. He is coached by his mother.

Istomin broke into the top-200 late in 2005 and finished the year at #196.

Istomin received the Asian Wildcard into the 2006 Australian Open where he played world number one Roger Federer. Federer won in three straight sets, 6–2, 6–3, 6–2 .