In this study, the applicability of enzymatic modification of milk proteins by transglutaminase enzyme in production of Ayran and the effects of enzyme addition on the quality criteria of product, were investigated. For this purpose, the enzyme addition to Ayran milk at two different steps of the production (just after the pasteurization and simultaneous addition with starter culture) and in two different incubation time with enzyme (at 50 ^oC 1 hour and 10 minutes), were tried. Ayran samples were kept at 4 ^oC for 20 days and analyzed on the 1st, 10th, and the 20th days of the storage. As a result, significant increase in viscosity and decrease in syneresis were determined. In Ayran samples produced from enzyme-treated milk, It was detected that transglutaminase did not cause significant changes on chemical properties of Ayran. Electron microscopic studies showed that enzyme- treated milk lead to obtain firmer microstructure in Ayran. Amount of enzyme used in this study was 1 Unit TGase/g milk protein. It was also determined that usage of this amount of enzyme concentration made no significant change in the flavour component of Ayran.