An inexpensive Wilhelmy balance based on a fiber optic sensor capable of sensitive surface tensionmeasurements has been designed and implemented. The system consists of a leaf spring conforming a cantilever structure and a bifurcated optical fiber acting as a laser beam deflection detector. Operated in a static way, it achieves a force measurement sensitivity of 0.154 V by N and a tension surface resolution of 0.1 mN/m. π-A isotherms of Langmuir films from insoluble amphiphiles 5 hexadecanoylaminofluorescein (fluorescein H-110) in water, were followed as a model system to characterize this instrument.