A trial was performed to study the effects of feeding a diet containing solid-state fermentation rapeseed meal (FRSM) replaced soybean meal (SBM) on growth performance and serum biochemistry parameters of ducks and then to determine the appropriate proportion of soybean meal replacement. The 75% rapeseed meal and 25% blood meal were mixed and inoculated with the Lactobacillus plantarum and Bacillus subtilis. Over the 21-day fermentation, isothiocyanates were reduced from 72.7 to 14.1 mmol/kg. A total of 1,280 fifteen-day-old Cherry Valley ducks were randomly allocated into 4 dietary treatments, 4 replicate groups of 80 ducks each for a 30-day feeding trial. In four treatment groups, fermentation rapeseed meal replaced soybean meal at 0, 33, 67 or 100%, respectively. Results showed that feed intake of ducks fed 100% FRSM was greater (p<0.05) than SBM and partial FRSM in both the finishing period (31-45 d) and entire feeding period (15-45 d). Daily gain increased gradually in the three treatment groups with augmenting FRSM over in the whole study period. In the growing period (15-30 d), compared with the SBM group, phosphorus and calcium content in serum from the FRSM group was improved (p<0.05). Total protein concentration was lower in ducks fed 100% FRSM than SBM and 33% FRSM (p<0.05). Concentrations of IgM were dramatically higher for animals fed 100% FRSM than in the SBM, 33% FRSM and 67% FRSM groups. In the finishing trail stage (31-45 d), only serum IgG content in 100% FRSM group was improved (p<0.05). Therefore, rapeseed meal fermented with Lactobacillus plantarum and Bacillus subtilis is a promising alternative protein source and fermented rapeseed meal can completely replace soybean meal in duck diet and potentially reduce the cost of duck production.