A population balance model expressing both drop breakage and coalescence was developed for poly(vinyl chloride) Microsuspension process with the measured drop size distributions (0. 1–, 1 µ, m) and volume-weighted mean diameter (0. 18–, 0. 22 µ, m) in a pilot scale double-stage high-pressure homogenizer. The prediction of the measured drop size distributions was satisfactory in terms of incorporating both breakage rate functions due to turbulent inertial and viscous forces with the dominance of breakage rate for inertial forces. However, a reduction in the pressure and the number of passes, and a rise in the dispersed phase volume fraction and premix size distribution resulted in enhancing the anticipated drop size distribution (D10, D90, and D90/D10). Additionally, as the emulsifier concentration improved, the distribution (D90/D10) increased due to the further decrease in mean D10 drop size than D90, despite the low emulsifier content. The breakage rate caused by viscous forces at the lowest concentration (CsCs=5 mmol/L) enhanced the predicted distribution (D90 and D90/D10). Due to the important contribution of viscous forces at larger dispersed phase volume fractions (φ, φ, =0. 622), especially when raising the number of passes, the estimated Sauter mean diameter declined and the distribution was further augmented, despite no increase in the mean D10 drop size. At the same time, the anticipated Sauter mean diameter improved at lower fractions (φ, φ, =0. 443). The stable droplets with unimodal size distribution (D90/D10 , = , 2. 8) were achieved at above one recycling pass and 13. 5 MPa under second-valve pressure equal to 3 MPa with the minimum effect of changes in dispersed phase volume fraction, emulsifier concentration, and suspension premix distribution.