Abstract: The aim of this study was to investigate the effect Tannic Acid (TA, 20 and 30 g kg-1 DM) on in vitro gas production and rumen fermentation of low and high fat sunflower meal (25 and 165 g kg-1 DM, respectively). Kinetics of gas production was fitted to an exponential model. The results showed that tannic acid caused to reduce the fermentable fraction (b) and gas production rate constant for the insoluble fraction (c) (p<0.05) and the lowest (b) and (c) was for low fat Sunflower Meal (SML) treated by 30 g kg-1 DM TA (102.5 and 0.01 mL h-1, respectively). The Organic Matter Digestibility (OMD) and Metabolizable Energy (ME) were decreased by TA treatments. Untreated SML had the highest ME and OMD (29.4 MJ kg-1 DM, 185.6 g kg-1 OM, respectively).The ammonia-N (NH3-N) concentrations and Short Chain Fatty Acid (SCFA) decreased (p<0.05) when SM treated with TA. Content of NH3-N was lowest for SML treated 30 g kg-1 DM TA (12.3 mg dL-1). Untreated sunflower meal had the lowest SCFA concentration and the highest Microbial Biomass (MB). The results showed, it may be that in vitro fermentation, gas production parameters and nutritive value of sunflower meal are influenced by tannic acid content.