Hydrometra procera is one of the semi-aquatic bugs found in paddy fields. I investigated the population fluctuation and food habits of the species to evaluate its potential as a biological control agent against Sogatella furcifera, Nilaparvata lugens, and Nephotettix cincticeps in a paddy field under sustainable cultivation. Through the present study, arthropods belonging to the following 7 taxa were sucked by the bug; Onychiuridae gen. sp., S. furcifera, N. lugens, N. cincticeps, Chironomidae gen. sp., Brachycera gen. sp. and Theridiidae gen. sp. Population density of the bug in the paddy field showed two peaks a year, in late June and in September. The former peak tended to synchronize with a peak of S. furcifera nymphs, while the latter peak with N. lugens, N. cincticeps, and collembolans. Therefore, main food resource of the bug should be these insects in the paddy field. Ovarian development of the bug under field condition revealed that the bug could be univoltine since females possessing mature ovary appeared once a year, from June to July. Rearing tests in laboratory at 22, 27 and 31℃ showed a developmental zero (T0) of 14.0℃ with a thermal constant (K) of 250℃-day from egg to adult for the bug, H. procera.