Composting livestock carcasses is a viable method for on-site treatment and disposal. Properly estimated carcass biodegradability is valuable for designing and controlling animal mortality composting systems. However, it is still difficult to assess the biodegradability inside composts. In this study, approximately 250kg of swine carcasses were composted in each of nine 2m X 2m weighable composting test units using three different envelope materials: corn silage, ground cornstalks, and ground oat straw. Total weight of compost material was measured monthly to observe the carcass decomposition trend with composting time. The most significant weight loss occurred during the first 6 weeks of composting. Biodegradability of the swine carcasses was estimated by comparing the mass of carcass remains after 16 weeks composting with the total carcass weight placed in the pile during the time of construction. Based on these results the influence of envelope material type on the biodegradability of swine carcasses was evaluated. The carcass decomposition within silage test units was only 66% of the initial carcass mass, while carcasses in cornstalk and oat straw test units decomposed 86% and 79% respectively.