The present study investigated children's understanding of the distinction between living and nonliving things and children's use of causal mechanisms. Children, aged 3, 5, 7, 9, and 11 participated. They were given a series of questions, which measured children's understanding of several biological properties, including growth, nutrient intake, overeating(overwatering) and underfeeding(underwatering), factors that affect plant growth, reproduction, and reincarnation. The results showed that children understood only a small portion of the distinguishing criteria at age 3 and improved with age. Nonetheless, many(about 45%) 11-year olds do not attain all the criteria. Also, older children employed causal mechanisms more frequently and relied less on the perceptual properties and more on their categorical knowledge when making an explanation. Among biological properties, reproduction was easiest for children to grasp, which was followed by growth and nutrient intake, and then overfeeding/underfeeding and factors that affect plant growth and reincarnation. The animal category was the easiest to understand and there was no difference between the plant and nonliving thing categories. Three- and 5-year olds (or 5- and 7-year olds) were different from other age groups respectively, and 7-, 9-, and 11 year olds tended to be grouped together when their knowledge on biological properties were compared.