Abstract: Laboratory rearing and simulated field overwintering of Isyndus obscuruswere conducted in Beijing in 1991-1992. It has one generation a year andoverwinters in adult stage. The eggs aggregate in the form of egg masses,and hatch in 12.1±1.0 days after oviposition. There are 5 instars in thenymphal stage and its development lasts for 61-83 days. The adults mate in8-30 days after emergence and oviposit in the following year. Not only its mo-rphology and changes in color after moulting in all stages, but also the bi-onomics were described. Experiments both in laboratory and in the field sho-wed that it's a promising predator and can prey on many species of forestinsects, such as Lymantria dispar Clostera anachoreta, Apocheima cinerarius, Ne-matus sp. , Ivela ochropoda, Cnidocampa flavescens, Dendrolimus punctatus, D.tabulaeformis, Malacosoma neustria testacea etc.

Key words: Isyndus obscurus Dallas, Bionomics, Predator