According to Official Guinness Records,
First player to score a double century in a One-Day International is Belinda Clarke (Australia) in a World Cup match against Denmark in Mumbai, India, on 16 December 1997.By the end of the match Clarke remained not out scoring a total of 229 runs off 155 balls scoring 22 4's.
For a complete list of 1997 records, please visit 1997 Guinness Records in India.