Serum complement is valuable tool in determining the health status of fish. This study was conducted to examine in vitro activity of serum complement as an indicator of innate immunity in four sturgeon species, Acipenser stellatus, A. baeri, A. nudiventris and Huso huso (Chondrostei: Acipenseridae). The Effects of different temperatures, concentrations and volumes of serum on alternative complement pathway activity were evaluated using standard haemolytic assays in four sturgeon species (A. stellatus, A. baeri, A. nudiventris and Huso huso). Results indicated significant relation between measured hemolysis and concentration, volume and temperature (p<0.05). Maximal hemolytic activity was exhibited at 100% serum in four sturgeon species. (p<0.05). Exposure of different volumes of serum from sturgeon species to RBCs exhibited volume dependent hemolysis (p<0.05). Maximal hemolytic activity was resulted in 30 μL of serum for all the sturgeon species. The highest hemolytic activity occurred at 4 °C for all the sturgeon species, but the hemolytic activity decreased at 37 °C. The results showed that the alternative complement pathway activity in sturgeon species serum may be affected by temperature, concentration and volume of serum that it caused an increase in non-specific immunity and the resistance to the outbreak of diseases.