Treatment of bacterial cultures with hemolymph collected from desert hairy scorpions (Hadrurus arizonensis Ewing, 1928, Hadruridae) resulted in a time- and concentration-dependent inhibition of bacterial proliferation. The hemolymph proved effective in inhibiting growth of both Gram-negative and Gram-positive bacterial species. Incubation of E. coli bacteria with hemolymph at different temperatures (20–40°C) showed that the antibacterial effects increased from 20–30°C, but the hemolymph was largely ineffective in killing the bacteria at 35 and 40°C. Incubation of E. coli with hemolymph at 25°C for different time periods revealed that the antibacterial activities were extremely rapid and resulted in killing of bacteria within 1–2 minutes of contact. Interestingly, the hemolymph exhibited no phenoloxidase enzyme activity, hemolytic activity against sheep red blood cells, or melanization activity, which is a common mechanism of immunity among many diverse arthropods. This study is the first characterization of immune function of hemolymph from any scorpion species.