The genesis of iron-spherules in granitoid rocks has been studied from the angles of crystallochemistry and thermodynamics. The authors hold that the iron-spherules are probably the terrestrial materials, and not all the extrater- restrial cosmic dust as considered by earlier workers. The iron core of the iron-spherule may be the reduced product of iron-bearing minerals in the course of metamorphism, oa- the remained iron of the iron-bearing basaltic basement rocks, oa- the native iron in iron-bearing basaltic magma having assimilated basement socks. With the evolution of granitoid magma, the reac- tion series of Fe-→FeO→Fe304 is gradually formed, and the sphericity which has the core of Fe and the rims of Fe0 and Fe304 is produced. The amount and characteristics of iron-spherules in granitoid rocks depend on the composition of the material source of granitoid magma, the oxygen fugacity and the temp;rature of granitoid magna, etc.