The study was conducted to determine the best concentration of Callistemon viminalis and Elephantopus mollis leaf extracts both as individual and combined preparations that inhibit the growth of Staphylococcus aureus and their efficacies in inhibiting S. aureus in-vitro. The experiments were done with five treatments and three replications. The ANOVA and DMRT were used to detect statistical differences among treatments. The study was done at the laboratory of the College of Veterinary Medicine, Benguet State University from November 10-14, 2014 and February 2-6, 2015. Three sets of experiments were conducted namely: Experiment A (C. viminalis leaf extract), Experiment B (E. mollis leaf extract), and Experiment C (synthesis of C. viminalis and E. mollis leaf extracts). In each experiment, four concentrations of leaf extract were used (25%, 50%, 75%, and 100%). The study made use of amoxicillin as the standard commercial antibiotic against S. aureus which was dissolved in 15 mL distilled water. It was concluded that the pure extracts of C. viminalis, E. mollis and the 75% crude extract synthesis of both plant extracts can inhibit the growth of S. aureus in-vitro although less effective as compared to amoxicillin. The use of pure decoction extracts of C. viminalis and E. mollis and 75% combined decoction extracts of both plants can be used as alternative treatments for S. aureus infections in remote areas where amoxicillin cannot be readily available.