A field trial was conducted during 2007-2008 crop season to study the effect of castor as a trap crop in cotton agroecosystem in relation to major insect pests. The treatments were 5, 10 and 15 rows of Bt cotton interspersed each with row of castor, respectively, sole crop of Bt cotton and castor. Based on the pooled data, the treatment comprising of 10 rows of Bt cotton interspersed with 1 row of castor registered low incidence of jassids, Amrasca bigutulla Ishida (0.76 nymphs/3 leaves); whitefly, Bemisia tabaci (Gennadius) (2.78 adults/ 3 leaves) and tobacco caterpillar, Spodoptera litura (Fabricius) (6.84 larvae/plant). The sole crop of castor recorded high population of whitefly (6.43 adults/ 3 leaves) and tobacco caterpillar (28.83 larvae/plant). No egg as well as larval population of American bollworm, Helicoverpa armigera (Hübner) was observed throughout the cotton-castor season.