Bambara groundnut (Vigna Subterranea (L) Verdc.) is one of the smart underutilized and neglected crops of African legumes. Due to cleistogamy, the crop has not been improved regardless of breeding efforts made by different research agencies, hence mutation breeding using gamma irradiation could be used for this crop improvement. Gamma irradiation is a mutagenic agent that induces genetic and phenotypic variability in crops. The optimum doses must be determined before starting a mutation breeding program. The four Bambara groundnut genotypes were treated with gamma irradiation at 0, 100, 200, 300, 400 and 500 Gray(Gy). The study aimed to determine the optimum mean of the lethal dose at 50% (LD₅₀) and growth reduction at 50% (GR₅₀), using a linear regression model. The analysis of variance showed that the growth parameters (seedling length, petiole length and biomass) are significant. The investigation of gamma irradiation on survival percentage, seedling length, biomass and leaves was also conducted. The LD₅₀ for NAMCREAM, NAMBLACK, NAMBROWN and NAMRED are 182, 251, 283 and 395 Gy respectively. The GR₅₀ for NAMCREAM, NAMBLACK, NAMBROWN and NAMRED are 202, 385, 423 and 446 Gy respectively. The optimum doses were determined and variation was observed in gamma-irradiated genotypes and growth parameters. The results from this study will be used for a large-scale mutagenesis plant breeding program.