The diamond back moth; Plutella xylostella (L.) was long considered a relatively significant pest. Its impact was overshadowed by such serious defoliators as Pieris rapae (Linnaeus). It attacks plants in the family Cruciferae causing serious damages. In this research for new insect naturally occurring antifeedant substances, spindle tree Euonymus europaeus (Celastraceae) seeds was assayed for antifeedant and/or insecticidal activities. The alkaloid fraction, isolated from the seeds of the spindle tree was found to be responsible for the significant antifeedant activity of this tree using crude extract against 4th instar larvae of the diamond back moth.