This study investigated the effect of the boric oxide (B2O3) content on the arc-erosion performance of silver (Ag)-based composite electrical contact materials, produced by powder metallurgy combined with mechanical alloying. Pure Ag and B2O3 powders were milled in a high-energy planetary-type ball mill for 5 h, to obtain a powder mixture that would be used in manufacturing the composites. Powder mixtures containing 5, 10, and 15 vol.% B2O3 were drawn separately into a cylindrical die, pressed, and sintered at 200 MPa and 800 degrees C. For each composition, a symmetrical contact pair configuration was created. Arc-erosion experiments were performed under the following testing conditions: operating voltage of 220 V, AC switching mode, frequency of 50 Hz, switching current of 5 A, and switching frequency of 60 operations/min. The relationship between the weight loss of the contacts and the number of cycles was investigated. Contact surfaces were examined by scanning electron microscopy (SEM). Chemical compositions near the arc were determined by energy-dispersive x-ray spectroscopy. The weight loss decreased with increasing B2O3 content up to 10 vol.%, indicating that the optimal arc-erosion performance (minimum weight loss) was obtained with 10 vol.% B2O3. Excessive B2O3 caused much more worn debris and increased the weight loss. SEM examinations of the contact surfaces showed that the size of the arc-affected zones generally increased with an increasing number of cycles.