Abstract: As we know, the mole-ratio is closely related to free formaldehyde in UF resin. The main explored subjects in this paper are concerned as follows; (1) the possibility of reducing the free formaldehyde in UF resin under the condition of constant mole-ratio and constant ratio of portion-wise addition of urea. (2) The relation between the amount of formaldehyde-release from particle board and the hot-pressing technique.