Efficient control of Tetranychus cinnabarinus (B.) is in challenge worldwide. Herein we report the use of an amphiphilic block copolymer, poly(ethylene oxide)-b-poly(caprolactone) (PEO–PCL), as a micellar carrier to make formulations of ricinine, a water insoluble botanical pesticide, and the tests of their physical properties and moreover the acaricidal activity on Vigna unguiculata (L). Compared to the formulations made from small molecular surfactant, e.g. Tween-80, the polymer formulations showed differentiated spreading property on T. cinnabarinus (B.) and V. unguiculata (L.) leaf surfaces, i.e. having slightly lower contact angle on the mite's integument. This contributes a relatively easy wash-off performance of the polymer formulations from the V. unguiculata (L.) leaf and meanwhile an enhanced protection to the plant in the simulated field trial. Our work thus suggests favorable characteristic of amphiphilic polymer in the future development of insecticides.