The present work describes a simple and sensitive spectrophotometric method based on the release of p-nitrophenyl butyrate (p-NPB) for the estimation of lipase activity. The method was optimized and validated in biphasic complex media containing methyl ricinoleate (MR) or olive mill wastewater (OMW), although it may be used for other biphasic media. Reaction mixtures containing substrate (2.63 mM p-NPB in sodium acetate buffer, 0.05 M and pH 5.6, with 4% (v/v) Triton X-100) and lipase are incubated at 37 ºC during 15 minutes. After this time, 2 mL of acetone are added to stop the reaction and the corresponding absorbances are measured at 405 nm in a microplate reader. A linear response was obtained for Candida rugosa lipase concentrations in the range of 0.0054 to 0.1 g L^-1 and 0.093 to 0.5 g L^-1 for MR and OMW media, respectively. The method revealed to be more sensitive for MR medium. This conclusion was corroborated by the detection and quantification limits, which were smaller for MR than for OMW medium. The method is precise for both tested media, according to the Horwitz criterion. Besides the simplicity of this method, it is sensitive and precise, and could be adopted for routine analysis, as a tool for screening and detection of lipase activity. In addition, the fact of measuring the absorbances of the samples in a microplate reader, allows to analyze a great number of samples at the same time and to achieve a considerable time saving.