During an ecological and biological study on the cabbage butterfly. Pien‘s rapae L., an ichneumonid parasitoid (Sinophorus xanthosfomus Garv.) was found parasitizing in the larva of the insect on the tested cruciferous plants (cabbage- cauliflower and canole). This finding is a first record in Egypt for this parasitoid on the target insect (P. rapae). The larval parasitoid was found from December to February. The percentage of parasitism in the first season of study reached 40. 44 and 20 % at the 25"1 of January 20050n cabbage. cauliflower and canola, respectively, while in the second season of study the peak of this parasitoid in the host larvae on 13m of January 2006 was 48 . 44 and 30 %, on the same host plants, respectively. Some biological aspects of this parasitoid were also studied under laboratory conditions (2012 C° and 75:5 % R.H.). The egg larval stage duration was 20510.45 days, the pupal stage duration 10.751025 days, the mating duration lasted 1580:024 minuets, male longevity 182530.31 days, female longevity 172610.27 days and sex ratio was 2.90:0.19 : 1 female/ male.