Transmission electron microscopy has been used to characterize Al segregation in Al0.1Ga0.9N and Al0.3Ga0.7N alloys grown by metal organic chemical vapor deposition on 6H-SiC. It has been found that an interlayer of AlGaN alloy with much higher Al content was formed at first, followed by normal growth of nominal composition of AlGaN alloy. In Al0.1Ga0.9N and Al0.3Ga0.7N films. dislocation lines were also found to have more Al segregated than those regions free of dislocations in the matrix. Furthermore, it shows that more Al atoms segregate to an edge dislocation than to a screw one.