The aim of this study was to investigate the effect of the primary material of urea formaldehyde adhesive on the physical and mechanical properties of the medium density boards. In this study, two types of urea formaldehyde adhesive based on formalin and urea formaldehyde condensates were used. The adhesives made with both primary materials had low molar ratio of formaldehyde to urea (grade E1). The effect of press factor on the four levels (8, 8.2, 8.4, 8.6 s/mm) and the amount of adhesive at four levels (9, 9.5, 10, 10.5) percent on the physical properties such as thickness swelling and mechanical properties including flexural modulus, elastic modulus and internal bonding of the resulted boards of two different types of adhesives were studied. The results showed that the resulting boards with formalin-based urea formaldehyde adhesive had the highest flexural strength, elastic modulus and internal bonding, and also the least percentage of thickness swelling compared to the boards made with the urea formaldehyde-based adhesive. By increasing the press factor, the boards made with formalin-based adhesive compared to the adhesive based on the formaldehyde condensate had the same performance in lower consumption percentage. The use of formalin, despite the high quality of the resulting boards, requires a special maintenance requirement in the industry, in comparison to the urea-based adhesive based boards, due to high temperature instability.