Plastic mulches are routinely used in intensive horticulture for increasing yield and earliness, controlling weeds, and improving product quality. In Mediterranean horticulture, plastic mulches allow vegetable and fruit production along the year. However, the disposal of polyethylene-based plastics is an environmental concern, and causes costs and difficulties to users and managers. New biodegradable films have been recently made available for mulch applications, and their biodegradation in-soil requires to be analyzed in-depth. The aim of this research is to develop a laboratory respirometric system, working under controlled conditions, to evaluate the biodegradability of these materials in the soil. The designed respirometric analyzer was tested during 90 days at 25°C with commercial mulch films made from modified starch (Mater-Bi, Biofilm) or polylactic acid (Bioflex), and a cellulose film (Mimgreen Paper). Conventional low-density polyethylene was used as the reference mulch film. The unit determined the aerobic biodegradation rate as the CO2 generated by the different materials into the bioreactors. After incubation for 90 days, Mimgreen Paper biodegradated by ca. 14%, while biodegradation was similar for the three plastic films tested and ranked around 10%. The CO2 generated at the bioreactor containing the polyethylene was very low. The respirometric system developed proved to satisfactorily register the biodegradation of the materials tested. Mater-Bi, Biofilm, Bioflex and Mimgreen Paper demonstrated to start an in-soil biodegradation process.