After taking different scientific measures during silkworm rearing for harvesting successful cocoon crop and for the production of good quality raw silk, cocoon growers are loosing their crops with traditional mounting system and environmental conditions. It is observed that high and low temperature and humidity conditions during larval spinning influence greatly on cocoon and silk production. To asses the post effect of cocoon formation and raw silk production on M12 (w) and Nistari (M) races, the present study was undertaken. Just after completion of fifth instar rearing, spinning larvae of both the races were collected and mounted on bamboo made chandrikes. Chandrikes were kept in three different small chambers of different environment containing high (28 ±1 °C temperature and 90 ±2 %R.H), medium (23 ±1 °C temperature and 75 ± 2%R.H), and low (18 ±1 °C temperature and 60 ± 2%R.H) temperature and humidity respectively. Different cocoon and silk characters like single cocoon wt., shell wt., S.R%, filament length, renditta, denier etc. were recorded and analysed. Both the races show inferior quality cocoons and silk filament with high melting percentage at high temperature and humidity. Spinning of worms at low temperature and humidity did not show significant difference with the control. So it is clear from this experiment that temperature and humidity of environment have direct effect on silk spinning and reeling performance.