i think it is greg rusedski with a 239.8 km/h
See related answer below.
The fastest racquetball serve was recorded by Egan Inoue. He served it at 191 miles per hour.
the fastest serve was 153 miles an hour
The record for the fastest ace is held by Ivo Karlovic who served a 156 mph (~251 km/h).
Taylor Dent, 2010 148mph, fastest female Venus Williams 2007 128mph
on 24th June 2009 I watched a 141MPH from Ivo Karlovicagainst Steve Darcis and he consistently served over 135MPH ! He also second served at around 120MPH throughout and one second serve was 126MPH - that must be a record?
The fastest racquetball serve was recorded by Egan Inoue at 191m.p.h. Brian Fredenberg has the second and third fastest serves at 187m.p.h. and 186m.p.h.
The fastest 1st serve was recorded by Andy Roddick at 155 MPH (248KPH), the fastest second serve is also held by Andy Roddick at 153 MPH (245 KPH). In the women's game the fastest serve is held by Venus Williams at 129 MPH (206 KPH).
Venus Williams holds the record for fastest serve recorded by a female at 127 mph.