We investigate the effect of particles dispersed in a Newtonian medium on the filament breakup of suspensions under extensional flow. In particular, we focus on the final stage of the breakup process: 10 mu m poly(methyl methacrylate) (PMMA) particles with 0-20 wt% are dispersed in silicone oil and the effects of the added particles on the thinning dynamics of the filament are observed with time-dependent changes in the minimum neck diameter (W). The particles decelerate the breakup process until the minimum thickness (W) of the filament becomes 5 d (d = 10 mu m: particle diameter), and then they accelerate the process rapidly until the pinch-off. When the thinning dynamics and filament shape of the 20 wt% PMMA suspension are compared with those of a silicone oil with the same viscosity and surface tension, the particles affect the thinning dynamics by changing the breakup velocity under W similar to 35 d compared with the viscosity-matched silicone oil. When the filament becomes thinner than W similar to 10 d, the particles induce different surface shapes compared with those of the viscosity-matched silicone oil. When the filament becomes thinner than W similar to 5 d, the roughness of the filament surface increases. Thus, the effect of the particles in the final stage of filament breakup is more complicated than that in the initial stage, and we demonstrate that the particles dispersed in a Newtonian medium induce complex behaviors in the final stage of filament breakup.