Abstract: To obtain effective biological materials against tobacco black shank (Phytophthora parasitica var. nicotianae), the inhibition effects of three brassica extracts and three isothiocyanates on P. parasitica var. nicotianae were detected by mycelium growth rate method and inhibition zone method. The results showed that:Comparing with the control, 1) three brassica extracts (Brassica rapa L., Brassica juncea L. and Brassica campestris L.) at different concentrations significantly inhibited the mycelial growth of P. parasitica var. nicotianae with the EC₅₀ values of 11.39, 9.18 and 5.88 mg/mL, respectively. Brassica campestris L. extract had an optimal inhibition effect on the mycelial growth of P. parasitica var. nicotianae. 2) Allylisothiocyanate (AITC) and methylisothiocyanate (MITC) at different concentrations also significantly inhibited the mycelial growth of P. parasitica var. nicotianae with the EC₅₀ values of 2.07 and 4.44 mg/mL, respectively. AITC had a better inhibition effect on the mycelial growth of P. parasitica var. nicotianae; however, PITC had no inhibition effect on the mycelial growth of P. parasitica var. nicotianae. In conclusion, three brassica extracts and two isothiocyanates (AITC and MITC) could effectively control P. parasitica var. nicotianae.