Castor, Ricinus communis L. (Malpighiales : Euphorbiaceae) is an important non-edible oilseed crop, the leaves of which also serve as primary food plant of eri silkworm, Samia cynthia ricini Boisduval. A study was undertaken to evaluate the effect of botanical insecticides viz., Neem oil and Karanj oil on the growth and silk production of plain white and brick red strains of eri silkworm during Kharif and Rabi, 2011-12 at Ericulture Laboratory of RARS, Palem. The experiment was conducted with 50 larvae per treatment with five treatments of botanicals and an untreated control. During fourth instar least larval weight of 0.38g was recorded in the plain white strain of eri silkworm larvae that were fed with karanj oil (5mL/lit) treated leaves followed by the larvae fed with 2 mL/lit karanj oil (0.46 g) and 10 mL/lit neem oil (0.5g). In brick red strain the weight of the larva was significantly higher compared to the plain white strains and this strain has shown some resistance to karanj oil treatment. Effective rate of rearing (ERR) varied from 76.84 to 89.9% in plain white strains, whereas in brick red strains it ranged from 79.88% to 91.46%. Comparatively shorter larval duration was recorded in brick red strains than plain white strains. In plain white strains, significantly higher weight was recorded in the cocoons formed out of worms fed with 3mL/lit neem oil (1.89g) and 2 mL/lit karanj oil (1.82g) treated leaves. In brick red strains, higher shell weight of 0.64g was recorded with control treatment closely followed by 2 ml/lit karanj oil (0.50g) treatment showing its loss of efficacy. The treatmental differences were significant with respect to fecundity and non significant differences were noticed with hatching percent.