By investigation of effects of rapid solidification by laser surface melting (LSM) on solidification modes and microstructures of stainless steels, it was found that characteristic massively solidified structure formed in laser surface melted specimens of a certain compositional range which could not be seen in conventional TIC weld metal. In the massively solidified structure it was seen that a certain orientation relationship between austenite and bulky ferrte did not exist. STEM analysis had revealed that no differences of compositions between austeinte and ferrite of this structure. The massively solidified structure only formed when cooling rate was reaching a certain critical value a limited compositional range. The critical cooling rate for massive solidification depended strongly on compositions of alloys and it was found that this critical cooling rate became larger with increasing the Creq/Nieq of alloys for the same iron content. From examination of mechanism of massive solidification, it was shown that massive solidification would be formed when maximum growth velocity of dendrite was slower than isotherm velocity and large supercooling took place in the liquid ahead of growing dendrite.