Bacteria with high resistance to various antibiotics, including Staphylococcus aureus, have posed significant challenges in healthcare. Some strains of Staphylococcus aureus have evolved into methicillin-resistant Staphylococcus aureus (MRSA). Ulva lactuca, a marine natural resource, is relatively unknown to the public but has shown potential for producing compounds with antibacterial activity. In this study, the method used was bioautography thin-layer chromatography (TLC), which identifies compounds responsible for forming inhibition zones against MRSA. Active compounds were separated using preparative TLC, and the isolated compounds were tested for purity and identified using UV-Vis spectrophotometry and FTIR. The antibacterial activity of the isolated compounds was evaluated by measuring the inhibition zones formed around the discs with a caliper. Based on the interpretation of UV and FTIR spectra, the compound isolated from Ulva lactuca was identified as belonging to the pigment group, specifically pheophytin. Antibacterial activity testing revealed that the average inhibition zone diameters at 25% and 50% concentrations were 10.38±0.25 and 16.49±0.07mm, respectively. ANOVA results showed a significant difference in antibacterial activity (P< 0.05) between the isolates at 25 and 50% concentrations.