The ecotoxicity of the neonicotinoid insecticides imidacloprid and thiacloprid to the soil-dwelling arthropod Folsomia candida was assessed under laboratory conditions. The tests were focused on the survival and reproduction of F. candida in OECD artificial soil (5% organic matter) after 28 days of treatment in the soil. Imidacloprid was found to be more toxic than thiacloprid. Median lethal doses (LC50s) for effects on survival were 0.84 and 3.5 mgkg⁻¹ dry soil for imidacloprid and thiacloprid, respectively, while half maximal effective concentration (EC50s) for effects on the reproduction were 0.82 and 0.55 mgkg⁻¹ dry soil, respectively. No observed effective concentration (NOEC) for effects on reproduction was <0.01 and <0.31 mgkg⁻¹ dry soil for imidacloprid and thiacloprid, respectively. Both neonicotinoids showed an adverse effect on F. candida, with severe effects on their survival (for imidacloprid), and reproduction (for thiacloprid), which can lead to population collapse with time. This study shows that both, imidacloprid and thiacloprid, can affect the survival and reproduction of F. candida at concentrations below their respective NOECs in the soil. Further studies under more realistic conditions are needed.