A comparative study of two different staining methods for estimation of yeast's viability is assessed by microbial flow cytometry. Propidium iodide (PI) a well known nucleic-acid binding vital dye exclusion is compared with light green (LG), a cytoplasmic function related vital dye widely used in histological, histochemical and immunocytochemical staining. The yeast model used was heat-killed Candida guilliermondii cells. The stained heat-killed bacterial population showed on the dot-plot flow cytometer analysis, a clear separation towards the green-orange (350-600 nm) for LG, and orange-red (550-725 nm) for PI on the fluorescence spectrum-zone channels. Both dyes showed by non-parametric Kolmcgorov-Smirnov, 99% of probability of difference between heat-killed and live microorganism's histogram-population, with a D = ranking from 0.50-0.64 for LG to 0.91-0.98 for PI. Higher cost and carcinogenic risk when handling PI, make LG a better choice for flow cytometry yeast viability tests.