Biodegradable bags were developed as an alternative to plastic bags. However, their degradation in environmental conditions has not been fully investigated and is often incomplete. Here, the decomposition of three types of biodegradable and one type of plastic bags commercially available in Croatia was analysed in different environments. Bags were exposed for six weeks in water, soil, air and compost, while the control groups were stored in room conditions. All types of bags were sampled twice, and different parameters of changes in mechanical properties were measured. Also, mechanical properties of the bags and microbial communities exposed in treated (pesticides and manure) and untreated soil were analysed. The research established significant differences in changes in mechanical properties between different types of biodegradable bags, with 'white' and 'brown' bags showing the best decomposition potential. As expected, the largest change in the structure and mechanical properties of all types of bags was recorded in compost, and the lowest in air and water. Treated and untreated soil showed a significant difference in the abundance and diversity of microbial communities. Higher diversity of microbial communities of the treated soil potentially contributed to the higher degradation of the two analyzed types of bags („white“ and „brown“), which indicates that the degradation of biodegradable bags could be slower in natural habitats.