The effects of high humidity and temperature on the economic characters in the 5th instar larvae of Chinese (C-102) and Japanese (J-101) varieties of the silkworm, Bombyx mori L. were investigated. The mean high humidity of 94% with the prevailing temperature of 23°C increased the larval weight by 11% each, cocoon weight by 20 and 13%, shell weight by 17 and 10%, fecundity by 8 and 11% and decreased larval mortality by 60 and 14% and pupal mortality by 16 and 62% for C-102 and J-101 respectively. The mean high temperature of 30°C with the prevailing humidity of 58% decreased the larval weight by 13, cocoon weight by 18, shell weight by 24 and fecundity by 48% in case of C-102 while in J-101 the same characters were decreased, respectively, by 19, 29, 28 and 42%. This treatment caused high larval and pupal mortality of 82 and 25% in C-102 and 89 and 53% in J-101. However, C-102 proved to be better than J-101 in both the treatments.