In-situ spherical icosahedral quasicrystal phase (I-phase) was fabricated in Mg-Zn-Y-based alloys by metal mold casting route. The effects of Mn and/or Cu on spheroidized process, morphology and microhardness of primary I-phase were studied in this paper. The results showed that the solidified morphology of I-phase depended on the stability of spherical I-phase during the subsequent growth and critical radius Rr of the spherical I-phase. Only when actual radius smaller than critical radius Rr can spherical IQC be formed. The effects of the fourth component and degree of undercooling on Rr were studied for the first time. Amazing spherical minisize IQC had been produced by improving cooling rate using a water-cooled copper mold. Multicomponent spherical IQC is hopeful of being strengthening phase to novel metal composites.