The poly (o-phenylenediamine) (PoPD) was synthesized from the monomer o-phenylenediamine in hydrochloric acid (HCl) using potassium dichromate as an oxidant by chemical oxidation method. The prepared PoPD sample was characterized by thermogravimetric analyzer (TGA) and scanning electron microscopy (SEM). The thermogravimetric analysis (TGA) results showed that a weight loss occurred. The weight loss as a result of the thermal energy applied to the polymer sample is 9.649mg which is 85.0% of the original polymer sample. The point of the greatest rate of change on the weight loss curve (point of inflection) is found to be 275°C and is the peak temperature of the degradation of the PoPD. SEM analysis showed that the PoPD sample has particle sizes ranging from 200µm-50µm at 360 magnification, 500µm-50µm at 1000 magnification, 200µm-50µm at 1550 magnification and 500µm-150µm at 2000 magnification which revealed more unevenly dispersed particles of the poly (o-phenylenediamine) polymer at different magnifications. Therefore poly (ophenylenediamine) has different particle sizes and is also thermally stable at a higher temperature of 150°C.