In this study, antimicrobial activity of five water soluble chitosan oligomers with different molecular weights were evaluated against Candida albicans, two gram positive (Staphylococcus aureus, Staphylococcus epidermidis) and four gram-negative (Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, Enterococcus faecalis) bacteria using microdilution method. The results showed that gram positive bacteria and Candida albicans were more susceptible against chitosan derivatives than gram negative bacteria. Chitosans with molecular weight above 3 kDa showed lower MIC values, indicating stronger activity of chitosan derivatives with increasing molecular weight.