Sodium azide (NaN3) has been used in many biological studies as a mutagen. In the present study, the morphological and cytogenetic effects of NaN3 on barley (Hordeum vulgare L.) seedlings were investigated. Seeds of barley were treated with different concentrations of NaN3 (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mmol/L) and applied for different periods of time Q and 4 h). Parameters investigated, except for the mitotic index, were determined on Days 7 and 14. Increasing concentrations of NaN3 affected germination rates on Days 7 and 14 following application for 3 and 4 h. Although the length of the roots and leaves was affected by treatment with NaN3 on Day 14 of the germination period, coleoptile length was affected by NaN3 treatment on Day 7. Increasing concentrations of NaN3 and increased treatment period decreased the mitotic index compared with the untreated control. The inhibitory effects of NaN3 on the mitotic index indicate that NaN3 can have genotoxic and mutagenic effects on barley seedlings.