An investigation was conducted into the effect of microstructural parameters on the cracking behavior which often occurred in the brass layer softfaced on an AISI 4140 steel substrate. Particular emphasis was placed on a role of the microstructural change, which mostly depended on heat input during softfacing, in the cracking phenomenon. Detailed microstructural analyses of the cracked region showed that cracks were observed to be initiated in the heat-affected region of the 4140 steel, and then propagated into softfaced brass layer, resulting in a surface crack. In the case of the lower heat input, the number of cracks was significantly reduced, although many pores were formed in the softfaced layer because of insufficient melting. These findings suggest that the proper heat input condition must be used considering cracking behavior and softfacing defects.