Abstract: Current study systematically investigated the interaction of two alkaloids, anisodine and monocrotaline, with organic cation transporter OCT1, 2, 3, MATE1 and MATE2-K by using in vitro stably transfected HEK293 cells. Both anisodine and monocrotaline inhibited the OCTs and MATE transporters. The lowest IC₅₀ was 12.9 njmol·L^-1 of anisodine on OCT1 and the highest was 1.8 mmol·L^-1 of monocrotaline on OCT2. Anisodine was a substrate of OCT2 (K_m=13.3 ±2.6 njmol·L^-1 and V_max=286.8 ±53.6 pmol/mg protein/min). Monocrotaline was determined to be a substrate of both OCT1 (K_m=109.1 ±17.8 njmol·L^-1, V_max=576.5 ±87.5 pmol/mg protein/min) and OCT2 (K_m=64.7 ±14.8 njmol·L^-1, V_max=180.7 ±22.0 pmol/mg protein/min), other than OCT3 and MATE transporters. The results indicated that OCT2 may be important for renal elimination of anisodine and OCT1 was responsible for monocrotaline uptake into liver. However neither MATE1 nor MATE2-K could facilitate transcellular transport of anisodine and monocrotaline. Accumulation of these drugs in the organs with high OCT1 expression (liver) and OCT2 expression (kidney) may be expected.