The antifungal activities of medium molecular weight chitosan and its hydrosoluble derivative salt N,N,N-trimethylchitosan were examined as both gel and as a solid protective coating against three common food spoilage fungi (Penicilliumsp., wild Aspergillussp. and one standard strain of Aspergillusflavus). The salt derivative is characterized by having permanent positive charges and is expected to have a higher antimicrobial activity than commercial chitosan. In gel form, the minimum inhibitory concentration (MIC) resulted in the same value for both polymers against all tested fungi (> 2.0 gl^-1). The derivative presented a significant fungistatic action against the Penicillium strain within the concentration range of 0.2 to 0.6 gl^-1. When applied as protective coatings on freshly cut cherry tomatoes, the commercial chitosan appeared to be more effective in forming stable films and preventing fungal infestation than its derivative. Less than 20‒25% of samples were infected after one week of incubation when compared to control (uncoated) and chitosan treated samples.