The effect of ball milling on the pressureless sintering of MoSi$_2$ was investigated. Ball milling was conducted at 70 rpm for 72 hours using different balls and vessels: one used tungsten carbide balls in a plastic vessel(referred as B-powder) and the other stainless steel ball in a stainless steel vessel(referred as C- powder). The powder was compacted with 173MPa and subsequently sintered at the temperature range of 1150 $^{circ}C$ and 1450 $^{circ}C$ in H$_2$, atmosphere. Sintered density was measured and scanning electron micrograph was observed. Over 90% of the theoretical density was attained at 1250 $^{circ}C$ within 10 minutes for C-powders, while the similar densification required a sintering temperature of 1450 $^{circ}C$ for B-powders. Such a difference in sinterability between B and C-powders was discussed in terms of the effect of particle size reduction and activated sintering caused by Ni and/or Fe introduced during ball milling.