Abstract: The morphology and effect on properties of coarse intermetallic compound in modified 3003 aluminum alloy were studied by chemical composition analysis, microstructure observation, micro-hardness testing, scanning electron microscopy observation and energy spectrum analysis, and the forming mechanism was discussed. The solutions of controlling the coarse intermetallic compound were proposed. The results show that there was coarse intermetallic compound with average size larger than 100 μm in modified 3003 aluminum alloy ingot. The average hardness of the intermetallic compound was 315 HV and much higher than that of matrix. The formation of the intermetallic compound was related to the segregation of iron, titanium and manganese elements. When the mass fraction of iron element in the modified 3003 aluminum alloy was controlled below 0.13%, the coarse intermetallic compound could be avoided.