Sb2O3, Sb-metal, Bi2O3 or Bi-metal, powders were mixed with MgB2 powder. Starting compositions were ((MgB2)(M2O3)x, x = 0.0025, 0.005, 0.015, and (MgB2)(M)y, y = 0.01, M = Sb, Bi. Mixtures were processed by Spark Plasma Sintering (SPS) technique. As obtained composite samples show high density, above 94% of the theoretical density. While the secondary phases indicate on similar reactions, samples show different behavior vs. addition type and amount. This does not directly correlate with the melting temperature of the addition. From the critical current density (Jc
) and irreversibility field (Hirr
) enhancement viewpoints, optimum additions are oxides for x=0.025, 0.005. Both oxides are improving Jc
at high fields, but Sb2O3 is effective up to 10 K, while Bi2O3 is up to 30 K. Metal additions are decreasing Jc
when compared to pristine MgB2sample.