The rate at which biodegradable plastic (BP) mulch films decompose in agricultural fields depends on environmental conditions. If degradation of used mulch film is insufficient for plowing-down, they impede agricultural work and get entangled in farm equipment. We developed a new technique to accelerate the degradation of BP mulch films in agricultural fields by applying an enzyme from a Paraphoma-like phylloplane fungus (strain B47-9). Spray treatment of the enzyme solution alone significantly accelerated film degradation, and the additional application of a moisture-retaining agent, carboxymethyl cellulose sodium salt (CMC), further accelerated decomposition. Commercially available BP mulch films started to break down one day after treatment with the enzyme solution and CMC. Within seven days of treatment, small tears in the film turned into long cracks, covering 6.2% of the total film area.