In this study, the effects of different size and rate of urea powder usage in particleboard manufacturing on the formaldehyde emission of the boards were investigated. Two different sizes (Large, Small) and five different rates of urea powder (1, 2, 3, 4 and 5%) were used for particleboard manufacturing. Urea formaldehyde (1.35 moles) adhesive was used for production of three layered particleboards. Formaldehyde contents were determined by perforator method according to EN 120. Furthermore, mechanical and physical properties including bending strength, modulus of elasticity, internal bond strength, surface stability, thickness swelling and water absorption of the samples were determined according to EN 310, EN 319 and EN 317 standards, respectively. Formaldehyde emission values were decreased with the mixing of the urea powder with chips prior to gluing and the produced boards had E0 grade in terms of formaldehyde emission. The size and rate of the urea powder were statistically effective on the mechanical and physical properties of the produced boards. In addition, all of the boards produced with small size urea powders satisfied the required standards for mechanical, physical and formaldehyde emission properties, except groups produced with 5% small size urea powder. It should be noted that slight decrease of mechanical and physical properties were observed with the loading of urea powder. As a result, it was determined that using of the small size urea powder provided better results than large size.