Chitosan and its oligomers N-acetyl chitooligosaccharides and chito-oligosaccharides prepared by deacetylation and chemical hydrolysis, respectively and have a broad antimicrobial spectrum to Gram-positive (Staph.aureus and List. monocytogenes) bacteria and Gram-negative (Sal.typhimurium). Staph.aureus, List. monocytogenes and Sal. typhimurium were isolated in lower percentages (23.3, 0 and 6.67%, respectively) from talaga cheese, followed by zabadi-baladi and kariesh cheese. This study focused on antimicrobial activity of chitosan and its oligomers by inoculation it and the isolated bacteria in yoghurt. 1% of chitosan completely inhibited the Staph.aureus, List. monocytogenes at 5^th and 3^rd day, respectively and Chitosan exhibited a bacteriostatic effect on Sal. typhimurium. while 0.1% of N-acetyl chitooligosaccharides and chito-oligosaccharides had reduced the count of List. monocytogenes and bactericidal effect on Staph.aureus and Sal. typhimurium. The antimicrobial properties of chitosan and its oligomers also, the perception of palatability to consumers toward it were discussed.