The aim of this study is to describe, briefly, graft union formation in relation with compatibility/incompatibility related growth characteristics between different clonal apple rootstocks and cultivars. In this trial, M25 (vigorous), M11 (semi-dwarf), B9 (dwarf) and P22 (very dwarf) clonal apple rootstocks and Pink Lady (late season) and Mondial Gala (middle season) apple cultivars were used as plant materials. The scions of apple cultivars were whip-grafted onto rootstocks in May, 2007 in order to observe graft union development. 100 plants were grafted for each combinations. Graft samples were taken on 15(th) and 30(th) day and every 30 days thereafter for a year. Samples of 5 graft unions from each scion/rootstock combinations were fixed in ethanol (70%). Transverse sections (20 - 30 mu m) were cut with a rotary microtome. All sections were examined under microscope and microphotograps were taken. In this research, in sections prepared from subsequent samples until 12 months of graft combinations were seen a good union. Successful graft unions were observed in 90 days samples in all combinations and no evidences for tissue incompatibility found in this study. Histologic observations showed a compatible graft union in relation to tissue formation between graft members which have different growing features.