Induced mutation is an efficient tool to improve a crop through creation of variability but it has been rarely exploited in improving bell pepper. This research was aimed to determine the lethal dose (LD₅₀) and effect of gamma rays and ethyl methane sulphonate (EMS) on germination, root length, shoot length, seedling length, speed of emergence and seedling vigor index derived from mutagen treated seeds of bell pepper cultivar 'California Wonder', to create variability for desirable traits. Seeds were exposed to different doses of gamma rays using ⁶⁰Co gamma cell at Bhabha Atomic Research Centre, Trombay, Mumbai, India. Another set of presoaked seeds were treated with freshly prepared solution of EMS. The treated seeds including control were sown in the nursery beds in a green house in completely randomized design (CRD) with 5 replications. Observations showed that germination percentage, seedling root length, seedling shoot length, speed of emergence and seedling vigor index decreases with increasing dose of gamma rays and EMS. Higher doses of gamma rays (19kR and 22kR) and EMS (2.0% and 3.0%) had profound effect on these variables due to seed injury and resulted in poor growth of seedlings. Based on probit curve, LD₅₀ dose for gamma rays and EMS were 17.8 kR and 1.6%, respectively. Higher gamma rays and EMS doses had negative effect on the morphological characteristics and growth parameters of the seedlings derived from mutagen treated seeds. Therefore, consistent dose of gamma rays and EMS can be tested in other varieties or lines of bell pepper to generate variability for novel selection.