The population density of the Cotton caterpillar, Palpita indica (Saunder) larvae was gradually increased until 10th October and then decreased rapidly after that time at the watermelon culture of rain sheltered house. After 15th October, many larvae went to soil and molted to pupae for the hibernation. Most of pupae were found in pF 2.4 soil moisture condition, but none in pF 1.5 hydro-morphic soil. Most of the pupae were found below 5cm and there was no pupa below 10cm from the soil surface. The sex ratio of the overwintering pupae was 1.09 : 1.00. For the monitoring of the cotton caterpillar adults using sex pheromone compounds, different mixture ratios of each pheromone compound were investigated with (E)-11-hexadecenal and (E, E)-10,12-hexadecadienal. Seven versus three ratio of (I)-11-hexadecenal and (E, E) -10,12-hexadecadienal was more attractive than any other ratio, and then followed by 6 : 4, 8 : 2, 9 : 1, and 5 : 5 mixtures. As a result of monitoring with 7 : 3 mixture of (E)-11-hexadecenal and (E, E)-10,12-hexadecadienal, occurrence peaks of cotton caterpillar adults showed 4 times per year. The first time of adult appearance was late July in 2000 and middle July in 2001 and the highest number was collected on late September.