Abstract: The cotton mealybug Phenacoccus solenopsis Tinsely has become an important alien invasive pest, and has caused serious damage to the cotton industry in Pakistan and Indian in recent years. It was found to infest in 2008 in mainland China, and infected some cotton plantations in several places, and would be a great potential threat to cotton industry of China. For presenting effective insecticides to control the cotton mealybug, toxicity of 14 insecticides to 3rd nymph of the cotton mealybug with leaf dipping method was determined in this paper. The results showed that the toxicity of lambda-cyhalothrin, profenophos, chlopyrifos, and avermectins was relatively high in 14 insecticides tested. With longer treatment time, the toxicity of avermectins, emamectin benzoate, spinosad and chlorfenapyr increased significantly. After 24 hours treatment, relative toxicity of the 14 insecticides from high to low was lambda -cyhalothrin, profenofos, chlorpyrifos, avermectins, phoxim, carbosulfan, spinosad, chlorfenapyr, beta cypermethrin, methomyl, emamectin benzoate, triazophos, petroleum oil, and rotenone respectively. After 48 hours treatment , those relative toxicity from high to low was lambda -cyhalothrin, profenofos, avermectins, chlorpyrifos, emamectin benzoate, chlorfenapyr, spinosad, carbosulfan, phoxim, beta cypermethrin, methomyl, triazophos, petroleum oil, and rotenone. Compared to 24 hours, the relative toxicity sequence of 48 hours varied a little.