Rubber wood was modified with both a combination of silica sol and glyoxal urea (S-GU), and a combination of silica sol and glyoxal melamine urea (S-GMU). The physico-mechanical properties were measured. Thermal properties, chemical molecular structure, and cellular morphology were analyzed via thermogravimetry (TG), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The weight percent gain (WPG) increased as the concentration of the impregnated aqueous solutions increased. The S-GMU treated wood exhibited a greater WPG than the S-GU treated wood at the same concentration. Anti-swelling efficiency (ASE), modulus of elasticity (MOE), and modulus of rupture (MOR) of treated wood increased as the WPG increased. The highest ASE value was 42.0%, for the S-20%GMU treated wood, which was higher than the S-20%GU treated wood. The MOR of the S-20%GMU treated wood was improved by 25%. Thermal analyses showed the thermostability of S-GMU treated wood increased. FTIR results indicated the presence of C-N and Si-O-Si bonds in the S-GMU treated wood, and the lignin and carbohydrates degraded to a certain extent. SEM imaging showed that the S-GMU was deposited in the cell lumen and cell wall. Therefore, this study produced evidence of an improvement in the physico-mechanical and thermal properties of S-GMU treated wood.