This study was carried out on 1-year old trees of '0900 Ziraat' variety grafted onto 'Kus kirazi', 'Kara idris', 'Sari idris', 'MaxMa 14', 'MaxMa 60' and 'Gisela 5' in order to determine their compatibility. For this purpose, total peroxidase activity was determined by spectrophotomery assay. Taking ground tissue samples were planned three times as before the grafting (beginning), and then 8 and 12 months after grafting. Total peroxidase activities of rootstocks before grafting varied between 10.80 Delta Ag.min. ('Kus kirazi') and 7.83 Delta Ag.min. ('Kara idris') and were found to be statistically important. The peroxidase activity of '0900 Ziraat' was 11.07 Delta Ag.min. and the closest value occurred in Prunus avium rootstock. The most different values occurred in rootstocks of 'Kara idris' and 'Gisela 5. The results showed that peroxidase activity increased in rootstock and graft scion. This increase had higher values in heterogenetic combinations especially in '0900 Ziraat'/'Gisela 5' and '0900 Ziraat'/'Kara idris' grafts. Peroxidase activity was decreased at the 12th month for all combinations. The highest value was obtained from '0900 Ziraat'/'MaxMa 14' combinaion with 29.17 Delta Ag.min. while lowest one was '0900 Ziraat'/'Kus kirazi' with 17.39. The findings showed that peroxidase activity could he used as a parameter in early determination of graft incompatibility.