Animal housing contributes a large proportion of greenhouse gases (GHG) and ammonia emissions in livestock systems. The diversity of the French cattle systems is huge mainly because of the many manure management systems (with or without straw). The aim of this study is to provide knowledge on GHG and NH3 emissions to propose mitigation options. During, respectively 4 (P1) and 6 (P2) weeks, two deep litters were accumulated beneath three dairy cows in a mechanically ventilated room, with different animal stocking densities; 9.7m2 per cow in P1 and 12.4m2 per cow in P2 . During accumulation of the litter, we continuously measured the emissions of CO2, N2O, CH4, and NH3. The deep litter in P1 was more humid (20.1% DM) than in P2 (27.2 %DM). The deep litter in P1 produced less N2O but more CH4 and NH3 than in P2. Means emissions were, respectively, 8214 g/day/cow, 0.433 g/day/cow, 713 g/day/cow, and 97 g/day/cow for CO2-C, N20-N, CH4-C and NH3-N in P1 and 8048 g/day/cow, 0.468 g/day/cow, 627 g/day/cow, and 56 g/day/cow in P2. These results (i) improve our understanding of emitting processes related to deep litters; (ii) highlight that too high animal stocking density on deep litter will lead to higher GHG and ammonia emissions. In that sense, both animal welfare and environmental issues recommend lower stocking densities for dairy cattle.