Abstract: 【Objective】 In order to provide a scientific basis for balanced fertilization, the effect of boron fertilization on growth and yield of rapeseed was studied and soil critical available B was determined based on field trials in main rapeseed product region of Hubei Province. 【Method】30 field trials of B fertilizer application to rapeseed were conducted in 2005/2006 growth season. The soil critical value of B deficiency was determined according to effect of B fertilizer on seed yield and soil available B content.【Result】The results showed that B application promoted the nutritive growth and yield components of rapeseed. The average increment with B fertilization was 428 kg/hm2 and the increasing rate was 28.0% for all 30 trials. Compared to control (no B treatment), about 70% trails received significant increase by B application, and the percentage of yield increment more than 500 kg/hm2 was as high as 26.7% for all trials. The results indicated that the yield increment by B application had significantly negative relationship with soil available B content. Based on the relative yield of CK/+B at 90 percent level, the soil critical available B was 0.58 mg/kg which was higher than that in the 1980s determined by the second nationwide general soil survey achievement.【Conclusion】The yield-increasing effect of B fertilizer on rapeseed is notable and the soil critical available B is 0.58 mg/kg in Hubei province at present time. According to the soil B deficiency criterion, it is necessary apply B fertilizer to about 80% rapeseed cultivated field in the main product region of Hubei Province.