Abstract: The relative toxicity of abamectin to the predator mites, Neoseiulus fallacis (Garman) was assessed in the laboratory. Eggs and female adults of the predator mites dipped into five different concentrations of abamectin were placed on bean (Phaselus vulgaris Linn) leaf disks treated by dipping into the corresponding concentrations of abamectin. The results showed that toxicity of abamectin to the adults of the predatory mites depended on the concentration of abamectin. Survival rate of N. fallacis female was reduced by 50% at 72 h after treatment with concentrations of 0.6 and 0.9 mg·L^-1. At concentration of 0.3 mg·L^-1, survival rate was significantly lower than CK at 144 h but recovered to the same level with CK at 240 h. Abamectin at the concentration between 0.3 and 0.9 mg·L^-1 significantly reduced reproduction of the predatory mite, but had no effect on the egg hatching. Moreover, abamectin at the concentrations of 0.3—0.6 mg·L^-1 had no effect on larval survival rate within 72 h, but did affect the survival of nymph. After 96 h, all nymphal predators died when the concentrations were 0.3 to 0.9 mg·L^-1. Further study is needed in the field to evaluate toxicity of abamectin to predatory mites and to develop abamectin-resistant N. fallacis for the control of the spider mites.