Abstract: This research was carried out on five important hazelnut cultivars (Tombul, Palaz, Kalinkara, Cakildak and Uzunmusa), which is in round shape group, between 1999-2001 years. Nut characteristics such as nut number per cluster, nut size, nut weight, shell thickness, kernel percentage, kernel weight, kernel cavity were investigated. Correlation coefficients among these characters, both direct and indirect effects were determined. In the result of this study it was found that nut number per cluster and kernel percentage increased; whereas nut size, shell thickness and kernel cavity size decreased. Connected with shell thickness increase, nut weight increased, but kernel percent decreased. Small nuts had thinner shell and higher kernel percentage.