The effect of heat input on the microstructure and mechanical properties of low nickel-high manganese stainless steel welded using a shielded metal arc was investigated. Six samples divided equally into two groups that represented the two distinct degrees of heat input were conducted: low heat (128 J/mm- 139 J/mm-165 J/mm) and high heat (182 J/mm -207 J/mm- 225 J/mm), respectively. These groups were subjected to microstructural analyses and tensile tests to see how heat input affected their joints' mechanical characteristics and microstructure evolution. In the second group, the high value of the ultimate tensile strength (UTS) was found in the case of the high-heat input (182 J/mm) sample. Macrostructure observations were made at the melting zone for each sample. In the case of low heat input formation, partial penetration was observed. However, in the case of high heat input formation, full penetration was observed in all samples treated to the various heat inputs. No defects, such as cracks or voids, were found. In addition, it was observed by increasing heat inputs that the average inter-dendritic spacing in the weld zone increased, which plays a significant role in the observed changes in the tensile characteristics of the welded samples.