The effect of the addition of Si to Nb-60at.%Ti alloy on the critical current density in the transverse magnetic field was investigated. The critical current density of Nb-60at.%Ti alloy aged at temperatures ranging from 350 to 550°C increases markedly with the addition of 0.5-2at.%Si. The α-precipitates as pinning points of flux lines become finer and dispersed more uniformly with the addition of Si, thus leading to the increase in the critical current density. By means of the aging at 500°C for 3hr after the cold-drawing of 98.4% reduction, the critical current density of Nb-58at.%Ti-2at.%Si alloy reached the maximum value of 6.0×104A/cm2 at 70 kOe.