The inclusion of raw rapeseed meal (RSM) in broiler diets is often limited due to the presence of anti-nutritional factors. Microbial fermentation has been proposed as an effective strategy to improve the nutritional value of plant-based protein sources. This study aimed to evaluate the effects of replacing soybean meal (SBM) with either RSM or fermented RSM (FRSM) on growth performance, gut microbiota, biochemical indices, intestinal morphology, nutrient digestibility, and cecal short-chain fatty acid concentrations in broiler chickens. A total of 300 one-day-old male Cobb 500 broiler chicks were randomly assigned to five dietary treatments and reared for 42 days. The experimental diets included a corn-SBM-based control diet; a diet in which SBM was entirely replaced with RSM; and three diets in which FRSM replaced RSM at 33.3 % (FRSM33), 66.6 % (FRSM66), and 100 % (FRSM100), respectively. Replacing SBM with RSM significantly reduced body weight gain and increased feed conversion ratio (P < 0.05). In contrast, complete substitution of SBM with FRSM mitigated these adverse effects, significantly improving growth performance compared with diets containing high levels of RSM (P < 0.05). The inclusion of FRSM in place of SBM significantly increased lactic acid bacteria counts in the crop and reduced coliform counts in the ileum (P < 0.05). Furthermore, birds receiving FRSM diets exhibited significantly lower serum concentrations of total cholesterol, triglycerides, very low-density lipoprotein cholesterol, and low-density lipoprotein cholesterol (P < 0.05). The jejunal villus height to crypt depth ratio and cecal concentrations of butyric and lactic acids were significantly higher in birds fed diets containing FRSM compared with those fed RSM or the SBM diet (P < 0.05). The apparent ileal digestibility of crude protein and ether extract was also significantly improved in FRSM diets relative to the RSM diet (P < 0.05). Under the conditions of this study, replacing SBM with FRSM improved growth performance, nutrient digestibility, gut microbiota composition, short-chain fatty acid concentrations, and intestinal morphology relative to RSM diets. Although FRSM did not fully match the growth performance achieved with SBM, it improved nutrient utilization and gastrointestinal health. These findings suggest that FRSM may serve as a functional alternative protein source to SBM by promoting gut integrity and supporting physiological health in broiler chickens.