The present study was carried out to evaluate lemongrass's antimicrobial activities and probiotic cultures' viability in frozen yogurt. The yogurt was prepared with two different commercial starters of probiotics [Lactobacillus acidophilus (LA-5), Bifidobacterium lactis (BB-12)], incorporation with Streptococcus thermophiles and two various concentrations of lemongrass powder or extract (0.5% and 1%). The data showed that lemongrass extract inhibited all microorganisms' growth at a concentration of 36 µl/mL for fungi species (Aspergillus niger, Aspergillus flavus and Penicillium spp.) and 48 µl/mL for bacteria species (Pseudomonas fluorescens, aeruginosa, fragi and Aeromonas hydrophila, caviae, sobria). Lemongrass powder or extract produced an alternative, stable color and stable quality of yogurt during frozen storage. Sensory evaluation of frozen yogurt with lemongrass powder 0.5% had acceptable quality characteristics with higher antioxidant effect (Thiobarbituric acid values 1.02 mg malonaldehyde /kg) after 30 days of frozen storage. The viability loss during frozen storage of commercial probiotic cultures Lactobacillus acidophilus (LA-5) and Bifidobacterium lactis (BB-12) decreased between 0.7, 1.15 and 0.76, 1.36 log CFU/g, respectively in all treatments. The population of these microorganisms remained above 10⁵ CFU/g