Helichrysum arenarium (L.) (Asterales:Asteraceae) Moench is a therapeutic plant which contains etheric oil, flavones and flavon glycosides, sterins, bitter substances and tannins having various coumarins. This plant is thought to have important characteristics such as diuretic effect, dropping stones and sand from the kidney, regulating digestive disorders, strengthening the immune system, and having antibiotic and antioxidant effects. Additionally, this plant is traditionally used in liver and biliary tract diseases and also shows anti-inflammatory and detoxifying properties. Model organism Galleria mellonella L. (Lepidoptera:Pyralidae) is an invertebrate species that is frequently used to study the effects of human pathogens and various pesticides, hormones, etc. on immune system. In our study, we examined the effect of various doses of H. arenarium on the hemocyte count and behavior of G. mellonella larvae. According to the findings obtained at the end of our study, H. arenarium caused an increase in hemocyte count with the injection of 0.25% and 0.5% doses compared to the untreated and DMSO groups. At the same time, the 0.25% and 0.5% doses showed a strong encapsulation-melanization response and an increase in phenoloxidase enzyme activity over 24 h compared to the other injected groups. Based on these results, H. arenarium extract has an anti-mitotic activity at high doses (above 0.5%). This effect may be due to the fact that the plant extract supports mitosis at a certain dose, while being toxic when exceeding it.