A simple CE based method was developed and validated for the determination of interferon alpha-2a in a pharmaceutical formulation. After optimization, the best results were obtained using 30 mmol L⁻¹ tetraborate buffer at pH 8.50 with 50 mmol L⁻¹ of sodium dodecyl sulfate, and using a diode array detector at 200 nm. The applied voltage was +25 kV, and the sample injection was performed in the hydrodynamic mode. All analyses were carried out in a fused-silica uncoated capillary with an i.d. of 75 μm and an effective length of 50.0 cm. Under these conditions, the analysis was achieved in less than 12 min. Linearity was obtained in the range 0.41–1.54 MIU mL⁻¹ (r ≥ 0.997). The RSD (%) and relative errors (%) obtained in precision and accuracy studies (intra-day and inter-day) were lower than 5%. Therefore, this method was found to be appropriate for controlling pharmaceutical formulations containing interferon alpha-2a.