To investigate the metabolism of linseed lignans in the rumen and its impact on ruminal metabolism, four healthy male Huainan goats were used in a crossover study. Following secoisolariciresinol diglucoside (SDG) crude extract treatment, the concentrations of SDG, enterodiol (END) and enterolactone (ENL) in both ruminal fluid and serum were significantly increased (P<0.01). Concomitantly, the pH value and ammonia-nitrogen concentration of ruminal fluid were decreased (P<0.05), and the concentrations of microbial crude protein and total volatile fatty acids were increased (P<0.01). Furthermore, testosterone and 3, 3′, 5-triiodothyronine levels in serum and ruminal fluid were both significantly increased, while the concentration of E₂ in ruminal fluid was decreased. Based on these observations, it is suggested that ruminal microorganisms were able to efficiently convert SDG to END and ENL, which were absorbed immediately. In return, SDG and/or its metabolites may facilitate the utilization of non-protein nitrogen and carbohydrates in the rumen.