The present study was conducted to investigate effective starter culture to improve biological activity of Asarum sieboldii. Antibacterial activity, antioxidant activity and reduction of enteric rumen methane production were used as criterions for biological activity. Ground A. sieboldii was added in MRS broth at 10% (w/v) and fermented by different starter cultures. Weissella confusa NJ28, Weissella cibaria NJ33, Lactobacillus curvatus NJ40, Lactobacillus brevis NJ42, Lactobacillus plantarum NJ45 and Lactobacillus sakei NJ48 were used for starter culture strains. Each starter culture was inoculated with 1% (v/v) ratio and fermentation was performed at $30^{circ}C$ with agitation (150 rpm) for 48 h. MRS broth for the control was employed without starter culture. Then the fermentation growth was dried and extracted using ethyl alcohol. The growth of starter culture was detected at NJ40, NJ42, NJ45 and NJ48. And the highest cell growth was found in NJ40. Antibacterial activity against to Staphylococcus aureus, Listeria monocytogens, Mannheimia haemolytica and Salmonella gallinarum were observed in the extract fermented by NJ40 and NJ45. All treatments showed antioxidant activities, however, there were no significant differences (p>0.05). In in vitro rumen fermentation, negative control (NC) and positive control (PC) were assigned to without extract and with non-fermented A. sieboldii extract. Significant suppression of gas productions were detected in positive control and treatments compared to negative control (p<0.05). However, total volatile fatty acid production was not suppressed. Significant methane reduction per total volatile fatty acid productions were found in positive control and NJ45 treatment (p<0.05). The present study suggested a fermentation of A. sieboldii using NJ45 strain could improve its biological activity and make possible for its use in bio additive for enteric rumen methane mitigation without suppression of animal productivity.