Viscosity change of melamine urea formaldehyde glue line was investigated with a thermo mechanical analyzer (TMA) used as a parallel plates rheometer. A small quantity of adhesive was placed between two wood disks of 10 mm in diameter and the initial glue line thickness was about 0.15 to 0.25 mm. During measuring process, the testing model was heated so that its temperature increased linearly with time at a rate of 10 ℃/min. In the meantime a constant force of 0.5 N was applied on the top of model to compress the glue line and some of the adhesive was squeezed out between the wood disks. The experimental results showed that the initial glue line viscosity (30 min at room temperature) was more than 10 4 Pa·s, much higher than that of a liquid resin. The viscosity change of a glue line with temperature and time could be described qualitatively by a dual equation. With the increase of temperature, the glue line viscosity decreased until a minimum viscosity was reached, after which rapid viscosity increase occurred due to the advancement of cure reaction. From the viscosity temperature curves, two important temperatures related to the hot pressing process of wood composites were obtained, i.e. viscosity inflection temperature T c, corresponding to the minimum viscosity, and gel temperatue T gel . The quantity of hardener played an important role in the glue line viscosity change. With 0.5, 1.5 and 3% NH 4Cl, T c were respectively 87, 76 and 71℃. Addition of a filler(starch) could modify rheological behavior of the glue line, which was demonstrated by an increase of the initial glue line viscosity and an augmentation of the viscosity inflection temperature T c. This research indicated that TMA was suitable for modeling hot pressing process and measuring in situ the glue line viscosity change during early stage of cure.