We investigated soil quality growth effects on Folsomia candida (Willem) (Collembola) in microcosm experiments. A high-quality forest soil (andosols) and pure sand were used as substrates in one experiment and soil quality was controlled by mixing the two soils using 25, 50, and 100% forest soil to sand (vol/vol basis). A higher forest soil to sand ratio increased microbial biomass N, total C (TC), and total N (TN) contents, soil respiration, and dissolved organic carbon (DOC). Collembolan body length increased with increasing proportions of forest soil. In another experiment using seven forest soils, collembolan growth was compared with soil parameters such as organic matter content, TC, TN, soil pH, microbial biomass (C, N, and P), and respiration. Growth was greater in soils with lower microbial biomass and higher microbial N/P ratio. Since higher microbial N/P indicated a higher percentage of bacteria] biomass, we concluded that collembolan growth reflected soil biological quality, especially bacterial activity.