Oxybenzone (BP-3) is a common ingredient in sunscreen. Its detection in marine ecosystems and demonstrated toxicity to various marine species has raised environmental concerns, yet little is known about BP-3 toxicity to macroalgae. Here, the effects of BP-3 (0.03, 0.1, 0.3, 1, 3, 9 and 27 mg/L) was investigated in two experiments: a chronic germination-inhibition study with Hormosira banksii and an acute study with mature Ulva lactuca. Results showed that at 72-h, 3, 9, and 27 mg/L BP-3 significantly inhibited H. banksii spore germination. The 10% effect concentration estimate was 0.363 mg/L BP-3. At 72-h, U. lactuca relative growth rate was 20-70% lower than controls in 0.1, 3, 9, and 27 mg/L BP-3 treatments. U. lactuca exposed to ≥0.3 mg/L BP-3 had lower chlorophyll a and b concentrations and higher lipid peroxidation than controls, with differences significant at ≥9 mg/L BP-3. Results suggest that BP-3 does not pose an acute risk to mature U. lactuca at the concentrations typically observed in environmental samples. Further studies are required to determine potential risks to U. lactuca associated with chronic exposure to environmentally-relevant concentrations. The toxicity data generated is informative for future risk assessments of impacts of BP-3 on temperate marine environments.