Mutation induction is considered as an effective way to enrich plant genetic variation, particularly for traits with a very low level of genetic variation. The objectives of this study were to evaluate the effect of different dosages of chemical mutagens on seed germination, seed viability and seedling growth characteristics and to identify optimum treatment conditions for chemical mutagens based on the LD 50 criterion in canola (Brassica napus L.). Two pretreatment conditions of soaking in distilled water and non-soaking, different concentrations of chemical mutagens, and four treatment periods were investigated. The effect of mutagen dosage on seed viability was also assessed using the tetrazolium staining test. Results revealed the significant effects of mutagen dosages and treatment periods on seed viability and seed germination as well as on seedling characteristics for all the mutagens tested. Additionally, it was found that increased dosage and period in each treatment led to significant reductions in seed viability for the tested mutagens. Pretreatment did not significantly influence most of the studied characteristics. The 0.8% ethyl methanesulfonate (EMS) for 6 h, 12 mM N-nitroso-Nethylurea (ENU) and 6 mM sodium azide for 8 h and 9 mM N-nitroso-N-methylurea (NMU) for 4 h were considered as optimum treatment conditions.