The 2005 İstanbul Cup was a tennis tournament played on outdoor clay courts.

It was the first edition of the İstanbul Cup, and was part of the WTA Tier III tournaments of the 2005 WTA Tour.

It was held in Istanbul from 16 through 21 May 2005.

* per team The following players received wildcards into the singles main draw: The following players received entry from the qualifying draw: The following players received entry as lucky losers: The following pairs received wildcards into the doubles main draw: Venus Williams defeated Nicole Vaidišová, 6–3, 6–2[1] Marta Marrero / Antonella Serra Zanetti defeated Daniela Klemenschits / Sandra Klemenschits, 6–4, 6–0