Mussels are an excellent source of phytosterols, which have many health benefits including reduction of the level of cholesterol in the blood. This study examined free sterols in cultivated blue mussels obtained commercially and from laboratory feeding experiments. Mussels were fed algae or the effluent from cultured finfish for 6 mo, and others remained unfed for 10 wk. Mussels feeding on effluent is of interest for integrated multitrophic aquaculture. Fish waste-fed mussels had significantly higher cholesterol concentrations (710 mg/kg) compared with algae-fed mussels (409 mg/kg) and locally cultivated ones (321 mg/kg). Algae-fed mussels had significantly higher campesterol compared with locally cultivated and fish waste-fed mussels. In algae-fed mussels, 24-nordeydrocholesterol decreased significantly, and in fish waste-fed mussels, the concentration of 24-methylenecholesterol decreased significantly. In fish waste-fed mussels, the cholesterol proportion was 50.9% of total sterols and other beneficial sterols were 49.1%, whereas in algae-fed mussels, cholesterol was down to 36.7% and other sterols were 63.3%. In summary, fish waste-fed mussels had significantly higher cholesterol concentrations and proportions compared with locally cultivated and algaefed mussels, and algae-fed mussels had higher proportions of beneficial phytosterols than fish waste-fed mussels.