An attempt has been made in this research work to probe the sequel of initial grain size of the steel and its impact on tensile strength. Low carbon-manganese steel in respect of initial grain size and final grain size has been deliberately investigated. Two steel samples having similar chemical composition were austenized at temperatures of 925°C and 1100°C respectively with same holding time in the box furnace followed by quenching. Initial microstructure at 925°C and 1100°C were calculated as 62.34 um and 124.4 um respectively. Just after heat treatment both the samples were prepared for tensile testing as per standard. UT machine was used with a cross head speed of 0.5 mm/min. The raw data obtained from the UT were analyzed stress and strain equations and stress-strain diagram was plotted by using origin software. It was concluded that the sample with initial grain size of 62.34 um showed high elongation curve and large plastic range. The large grain sized samples having initial grain size of 124.4 um, the tensile curve showed a short elongation curve with low plastic range.