Livestock farming is a significant contributor to anthropogenic greenhouse gas emissions. A major source of these emissions is the methane produced through enteric fermentation, which occurs during the digestive process of ruminant animals. Feed additives have been identified as an effective way to reduce enteric methane emissions. However, not all feed additives are practical or widely available. Therefore, alternative additives need to be identified for local or regional use. This study aimed to evaluate the effect of limonite and tannin on enteric methane generation during in vitro rumen fermentation. The experiment involved adding different concentrations (2 mg, 10 mg and 20 mg) of limonite and tannin to rice straw (200 mg) in rumen liquor. A control treatment without additives was also included. The results showed that the treatment with 2 mg, 10 mg and 20 mg of limonite significantly reduced methane production by 80%, 91%, and 94%, respectively, compared to the tannin treatment, which only reduced methane by 59%, 78% and 87%. This suggests that limonite could be a more effective additive for reducing methane emissions. Limonite has been used in livestock production to improve animal growth performance, primarily due to its high iron and mineral content such as calcium and manganese. This study suggests that limonite could also reduce enteric methane emissions in addition to enhancing animal productivity.