Mn bearing dispersoids play a very important role in recrystallization and solution-aging process in AlMgSi alloys. Plenty of research have been made on the effect of the disperoids on recrystallization and quenching sensitivity behaviour in these alloys. But study on the nature of these dispersoids is very limited. With an idea to understand the nature of these dispersoids and hence to control their size and distribution, this study was performed. It was found that in AlMgSi alloys, the size of the dispersoids is dependent on Mn/Fe ratio, the higher the Mn/Fe ratio, the smaller the size of the dispersoids. A crystal structure transformation with Mn/Fe ratio change was also found in these dispersoids. With higher Mn/Fe ratio, these disperoids have a simple cubic crystal structure while with lower Mn/Fe ratio they have a BCC structure. A critical Mn/Fe ratio for this change was found to be 1.6 in studied alloys. Results were explained with consideration of the originating local surroundings and heat treatments.