Abstract: Germination safety to cucumber seeds(two cultivars Zhongnong No.8 and Changchun Mici),coated with 20% o-allylphenol seed coating formulation at the ratio of 1∶ 30~1∶ 90(ratios of seed weight)was tested by ISTAs blotter paper method.The results showed that o-allylphenol seed treatment is safe to seed germination,the germination ratios for both cultivars were 95.75%~97.75% and 80.00%~84.25%,respectively.Based on the PDA test,the control effect of seed disinfection was up to 66.67%~100%.Hyphal growth rate test and microscopy demonstrated that o-allylphenol markedly inhibited the growth of two harmful soil - borne pathogens,Pythium aphanidermatum and Rhizoctonia solani,with EC50 value ranging from 27.59 to 34.16 μg/mL.The o-allylphenol treatment resulted in abnormal appearance of fungal hypha,such as broken and cavity.When the cucumber seeds were treated with 20% o-allylphenol seed coating formulation as previous ratios before inoculated with P.aphanidermatum and R.solani, the disease control efficiency was 73.31%~100% and 85.16%~100%,respectively.The control efficacy to both cucumber seedling diseases rose as the o-allylphenol concentration increased.The efficacy was equal or superior to that of regular dressing treatment with thiram.