Chasing a 125 run target the Lankans led by former Skipper Shashikala Siriwardene completed chase in 39.2 overs losing just 4 wickets in the process.
Siriwardene scored an unbeaten 42 off 72 deliveries while Yashoda Mendis contributed with 27 runs.
Earlier after opting to bat first West Indian women were bundled out for 124 runs in 42.3 overs. Stafanie Taylor top scored for the visitors with 43 while opener Kycia Knight chipped in with 28.
Shashikala Siriwardene was the pick of the bowlers capturing 4 wickets for 30 runs. Maduri Samuddika conceded just 16 runs in her 9 overs picking up two wickets.
Lankans squared the series 1-1 after West Indians won the tournament opener on Wednesday. The third ODI of the series will be played on Monday at the R Premadasa Cricket Stadium.