Abstract : This study evaluated the impact of a feed additive mixture (comprising benzoic acid, saponin, prebiotics, and minerals at 0.5%) on greenhouse gas emissions during pig manure storage in laboratory-scale slurry pits. Compared to the control, the group fed with additives exhibited a higher average CO2 emission rate (51.7±22.9 g/day/m3-slurry vs. 29.4±2.9 g/day/m3-slurry), though this difference was not statistically significant (p>0.05). However, the CO2 emission reduction rate over time was steeper with the additive. For CH4, the average emission rate was 1.5±0.9 kg/day/m3-slurry with the additive and 1.0±0.4 kg/day/m3-slurry in the control, with no significant difference (p>0.05). While the additive group initially produced more CH4, this trend reversed later in the experiment. These findings suggest that the potential of feed additives to reduce CO2 and CH4 emissions may become more apparent over longer experimental periods. In contrast, N2O emissions were significantly lower with the additive (6.2±2.5 mg/day/m3-slurry) compared to the control (36.0±15.1 mg/day/m3-slurry), representing an approximately 81.7% reduction (p<0.05). This effect was most pronounced during the early stages of manure storage. Consequently, feed additives effectively mitigate N2O emissions early in the storage process. Given the relatively short study duration of 55 days, further research is warranted to assess greenhouse gas emissions over extended periods of pig manure storage.