Abstract: With High Performence Liquid Chromatograph (HPLC), a quantative analysis of azadirachtin of neem seeds collected from neem trees that were introduced from Togo, Africa, now successfully cultivated in Wannin county, Hainan Province, China, as well as the test of insecticidal activity of the seed extracts have been conducted in the laboratory. The results showed that the air-dried seeds contained azadirachtin up to 0. 48%. The methanol extract with a recovery rate of 16. 39% from the neem seeds contained azadirachtin at 2. 94%. F3-5, a fraction of the methanol extract containing azadirachtin at 0. 883% was significantly effective against the 4 - 5th instar larvae of Asiatic corn borer,Ostrixia furnocalis when administered at a concentration of 113 ppm mixed with an artifical diet,and all the larvae developed malformation and died or became so call "permanent larvae" when treated at a concentration of 500 ppm. Arter eating or coming in contact with leaves trteated with 2%of F3-5, all the 4th instar larvae of the diamondback moth, Plutella xylostella were inhibited in their growth and development, malformation and death following. Besides the F3-5, other fractions of the methanol extract containing no azadirachtin e. g. F1-2, F6-15 and Fm, also showed similar bioactivity against the two insect pests, this is worthy of futher studies.