The paper presents the formation of multicomponent nanogranular FCC supersaturated solid solution containing a large amount of boron (B) in coexistent with small amount of nanoscale BCC phase after full crystallization of an amorphous (Fe0.25Co0.25Ni0.25Cr0.125V0.125)83B17 alloy. The metastable FCC phase remains unchanged at temperatures up to 1073 K. The unusual formation of an FCC single phase from the residual amorphous phase is presumably due to the suppression of long-range redistribution among the constituent elements with strong bonding atomic pairs and suitable atomic size differences, which can be regarded as a high entropy effect. With further increasing temperature, the solid solution decomposes to FCC + Me3B2. It is notable that the formation of only an FCC solid solution saturated with B from the residual amorphous phase is the first in as-cast and rapid solidification states.