Experiments are conducted for studying the slug breakup mechanism for three different liquid pairs in a serpentine minireactor of i.d. 2 mm. Liquid pairs used are kerosene-water (K-W), toluene-water (T-W), and jatropha oil-methanol (O-M). Two liquid pairs have a density ratio close to 0.8; however, they have widely varying viscosity ratios. The other two have a viscosity ratio of 0.6 but different density ratios. Flow patterns observed for all liquid pairs are categorized into four different groups, namely, slug flow, slug with droplet flow, intermittent slug flow, and droplet-dispersed flow. For higher dispersion to continuous phase viscosity ratio, long viscous thread formation is noticed, which leads to drop disintegration. However, for low dispersion to continuous phase viscosity ratio, the mechanism of formation of small droplets from slender slug takes place at a low Ohnesorge number.