This study was conducted to determine 4th, 5th, and 6th grade Turkish primary students' conceptions about the particulate nature of matter via a test. The test consists of 36 items related to the changes of microscopic properties of solid, liquid and gas matters during phase changing, cooling, heating and pressing of them. The sample of the study consists of 411 students, 139 of them are from grade 4, 121 of them are from grade 5 and 151 of them are from grade 6. The answers given to test have shown that the understanding levels of students in all grades about the microscopic properties of matter are quite low; they had little knowledge or misconceptions about the microscopic properties of the particles such as the order of the particles, spaces between particles, the number of particles, the size of particles and the movement of the particles; and progression of students' conceptions on the particulate nature of matter is multifaceted. (Contains 1 table.)