Investigations were carried out to assess the efficacy of Sikkim Bacillus thuringiensis isolates against lepidopteran insects viz., Cabbage leaf webber, Diamond Back Moth and bioassay were also done to assess the safety nature of Bt to silkworm. Bacillus thuringiensis isolates of Sikkim (Thirty five isolates) were assessed. Among these isolates mortality of each isolate was varied from insect to insect. The mortality of 86.67% was registered by the isolates 1554/b, 1526B/b and 1598d against Cabbage leaf webber. The isolates 6a4, 1598a, 1526B/b, 1622A/a and 1642A/a recorded maximum (93.33%) mortality against Diamond Back Moth. Whereas, 93.33 and 90.00 per cent mortality was recorded in 1620b and 1598d, respectively, against silkworm.