Plastic pollution has become a global environmental issue, with between 22 and 48 millions of tons of plastic waste accumulating in the environment annually. Transitioning from conventional plastics to biodegradable materials for single-use items could limit this accumulation, but the degradation advantage of biodegradable material over plastic lacks empirical evidence from in situ experiments. Here, we compared the short-term degradation of seven single-use items (e.g., shopping bags, take-away boxes), made from plastic and biodegradable materials, in both marine and terrestrial environments. Biodegradable items tended to degrade faster than their plastic counterparts, but this advantage occurred in less than half of the situations tested (6 out of 14 situations). Notably, biodegradable items degraded faster than plastic counterparts more often in the terrestrial (5 out of 7 items) compared to the marine (1 out of 7 items). Interestingly, biodegradable items made of plant-based materials, such as bagasse and cellulose, generally degraded more rapidly than plastic, while those made of polylactic acid rarely degraded faster than plastic. We conclude that biodegradable single-use items should not be disposed of in the environment and require adequate waste management, and we encourage future research on the long-term degradation of biodegradable items in a range of environments.