High-performance liquid-chromatography method was developed and validated for the determination of impurities (Related Substances) of Mycophenolate mofetil in tablets and capsules using Photo diode array detector. The mobile phase was a combination of Triethylamine buffer (pH 5.3) and acetonitrile in the ratio of 65:35 and wavelength set at 250 nm. Retention time of Mycophenolate mofetil and its impurity as Mycophenolic acid was found to be approx. 21.31 and 5.79 minutes respectively. Linearity of the method for Mycophenolate mofetil and its impurity as Mycophenolic acid was found to be 0.4 to 24.163 μg mL-1 with the correlation coefficient of 1.000 and 0.9999 respectively. This method was validated accordingly to International Conference of Harmonization guidelines. Qualification was alone by calculating area of the peaks and peak purities. The analytical solution of Mycophenolate mofetil also has shown stability for 24 hrs at 5°C and 25°C. Present method can be applied for the impurity profiling and stability studies of Mycophenolate mofetil in tablet and capsules formulations without interference of the excipients present in the particular formulations