An ellipsometric technique is described for measuring the uniaxial birefringence of Langmuir-Blodgett films. Through the use of certain assumptions about the film properties, it is found that only a small number of samples are required. The results for fatty acids are compared with those for an earlier method, and good agreement is obtained. It is also shown that the use of a uniaxial model leads to a significant improvement of the accuracy of fit. The birefringences of two dyes are also measured.