The Lavandula angostifolia is a medicinal plant that has the property of strengthening the immune system. In the present study, the effects of different levels of L. angostifolia extract on growth performance, survival rate and blood indices of the grass carp (Ctenopharyngodon idella) (11.01 ± 0.05 g, 15.5 ± 0.3 cm) was investigated. The fish were didtributed in 4 treatments (0 (control), 0.1% (T1), 0.5% (T2) and 1% (T3)). The fish were fed for 8 weeks. The results showed highest and lowest weight in both leaves and lavender groups in T3 and control group, respectively (p 0.05). The highest and lowest HSI was observed in control and T2 groups. No mortality was observed in the groups. The hematocrit, hemoglobin, RBC, WBC had significant difference (p 0.05). The levels of lysozyme, IgM and globulin in experimental treatments were significantly higher than control (p < 0.05). In general, the extract of common lavender has a positive effect on improving the biological status of grass carp
