The effect of ventilation rate (VR) on ammonia and greenhouse gas emissions from co-composting dead hens mixed with hen manure was quantified. Three VR levels of 0.9, 0.7, and 0.5 m³ h^-1 were evaluated. Gaseous concentrations were measured using a multi-gas infrared photoacoustic analyzer, VR was measured with flowmeters, and the gas emission rate was computed from the VR and gas concentration. Decomposition of the carcasses over the 11-week composting period was greater than 88%. VR was found to significantly affect NH₃, CO₂, and CH₄ emissions (p < 0.05). Specifically, cumulative emissions per kg of initial matter for VR of 0.9, 0.7, and 0.5 m³ h^-1 were, respectively, 2.4, 2.0, and 1.2 g NH₃; 78, 66, and 42 g CO₂; 120, 90, and 52 mg CH₄; and 6.4, 6.1, and 5.1 mg N₂O. Hence, the study results suggest that the ventilation rate can be adjusted to reduce NH₃ and GHG emissions from animal mortality compositing.