N-dodecylchitosan, N-(p-isopropylbenzyl)chitosan and N-(2,6-dichlorobenzyl)chitosan were the most active against B.cinerea, with EC50 values of 0.57, 0.57 and 0.52 g.L-1, respectively. Against P. grisea, N-(m-nitrobenzyl)chitosan was the most active, with 77% inhibition at 5 g.L-1. O-(decanoyl)chitosan at mol ratio of 1:2 (chitosan to decanoic acid) was the most active compound against B. cinerea (EC50 = 1.02 g.L-1) and O-(hexanoyl)chitosan displayed the highest activity against P. grisea (EC50 = 1.11 g.L-1). Some of the derivatives also repressed spore formation at rather high concentrations (1.0, 2.0 and 5.0 g.L-1).