Biology of Piesmopoda obiquifasciella a leaf stitcher of amaltas (Cassia fistula) was studied in the laboratory during 1996-97. Studies on the biology showed that the fecundity of a single female moth was on an average 37.71 ± 0.91 eggs with maximum of 45 and minimum 30 eggs. The oviposition, incubation, larval and pupal periods lasted for 1-3, 3-5, 8-18, 6-18 days, respectively while the adults remained alive for 4-17 days. There were seven generations in a year with an average life cycle of 1st, 2nd, 3rd, 4th, 5th , 6th and 7th generation was 32.5, 27,5, 26,5, 23.0, 27.5, 37.5, and 44 days in April - May, May - June, June - July, July - August, August - September, September - October and November - March, respectively. The pest hibernated in larval as well as pupal stages during December - February at 13.85 ± 3°C (maximum), 4.81 ± 0.69°C (minimum) temperature and 68.5 ± 6.58% relatively humidity. An inverse proportion was found between temperature and longevity of life span. High temperature combined with high relative humidity caused more profound impact on lessening life span rather than high, temperature singly.