The solubility, stability, and synergistic activity of mandarin oil, extracted from peels of Citrus reticulata Blanco, combined with rotenone (extracted from roots of Derris elliptica (Roxb.) Benth.) for use against citrus red mite, Panonychus citri (McGregor), were measured under laboratory conditions. Results showed that the solubility of rotenone in mandarin oil was 2.29% (W/W). A positive synergistic acaricidal activity against citrus red mite occurred at a 7:3 ratio of 50% lethal concentration (LC 50 ) of rotenone to mandarin oil, with a synergistic coefficient of 403.71. At ambient conditions, a degradation rate of 71.99% over 14 days was found for rotenone in mandarin oil, which was markedly higher than the rate of 61.44% in benzene. Experiments on mandarin oil revealed a 2.48% extraction rate of rotenone in mandarin oil compared to an extraction rate of 1.47% in benzene solvent. When used against adult red mites, the mandarin oil rotenone extract had an LC 50 of 0.88 mg/mL which is considerably more toxic than the LC 50 of 4.22 mg/mL for the benzene extract.