We studied and quantified the elimination of sunflower oil from a wastewater influent using a biological treatment by activated sludge. Estimation of the biodegraded material was obtained doing a mass balance, and we conducted a follow-up of the different operational parameters and design. We delivered information about the operation of a system for treatment by activated sludge fed with an influent with sunflower oil and saccharose. The influent was previously agitated before entering the effluent sludge in a lab-scale plant. The working range for oil concentration was 100 to 850 mg/L in the influent. Biodegradation was in the range of 60% to 51%. The process works better with a high initial concentration of biomass (7500 mg/L) in order to absorb the impacts caused by the oil on the microorganisms. The lowest total suspended solids concentration was 4500 mg/L. The elimination of sunflower oil in biodegradation and flotation was on the order of 90%.