Abstract: By using slide-dip bioassay method under laboratory condition, an investigation was made on the lethal effects of scopoletin, bisdemethoxycurcumin (BDMC), and their combination at an optimal mass ratio (7:6) of scopoletin to BDMC against the adult females of Tetranychus cinnabarinus Boisd. A timedose mortality model (TDM) was established, which passed the HosmerLemeshow test. The sensitivity of the adult females to the concentration change of the acaricides was in the sequence of scopoletin > optimal mass ratio of scopoletin to BDMC > BDMC. The peak mortality of the female adults was found at 32, 28 and 32 h after treated with BDMC, scopoletin, and their combination at the optimal mass ratio, respectively. The values of the LC₅₀ and LC₉₀ at 48 h after treated with BDMC, scopoletin, and their combination at the optimal mass ratio were 0.3324, 0.2035 and 0.2195 mg·mL^-1, and 2.1198, 0.9521 and 1.1617 mg·mL^-1，and the median lethal time (LT₅₀) of BDMC, scopoletin, and their combination at the optimal mass ratio was 7.4, 6.0 and 6.1 h at the concentration 1.0 mg·mL^-1, and 6.4, 4.8 and 5.0 h at the concentration 2.0 mg·mL^-1, respectively. The acaricidal activity and time-dose response of the optimal combination of scopoletin and BDMC were closer to those of scopoletin, suggesting a synergistic acaricidal activity of the combination of scopoletin and BDMC, which was worthy to be developed for application.