We describe the application of a nephelometer to in situ, real-time measurement of the integrated backscattering coefficient &sgr;bs of cloud drops. For thin and moderately thick clouds, this quantity is related to the cloud albedo A, for 0¿ zenith solar radiation, through the relation A=&sgr;bsL, where L is the geometric cloud thickness. The instrument was used in a field experiment on El Yunque peak in Puerto Rico. The measured &sgr;bs values are in agreement with results of Mie theory calculations, using independently measured cloud drop concentration and size distribution.