The mechanism of drop breakup inside SMX static mixers in the laminar flow regime was studied using experimental observations and computational fluid dynamics (CFD). The deformation and breakup of a single drop was simulated using the volume of fluid (VOF) model. It was observed that drops break up after collision with the leading edges and cross-points of the bars in the SMX static mixer. It was found that drop collision with the bar cross-points of the SMX static mixer elements is most effective for drop breakup. Elongation and folding result in drop breakup at the cross-points.