The shoaling and breaking of an internal solitary wave of depression on a uniform slope were studied experimentally. The waves were generated with as large an amplitude as possible while minimizing mixing at the generation site, thus maximizing the amount of energy propagating onto the slope in the experiment. Various bottom slopes, fluid layer thickness ratios, and density ratios were investigated. The mechanism leading to breaking was examined with flow visualization and particle image velocimetry. Since the layer thickness ratio primarily controls the length (LW) of the solitary wave (for a given amplitude a), it is found that the ratio of LW and the characteristic length of the slope LS determines the amount of energy reflected from the slope. The mixing efficiency of the breaking event, defined as the ratio of the increase of potential energy divided by the amount of wave energy lost at the slope, peaks at a maximum of 25% when LW/LS=0.5, with a decrease in efficiency for points on either side of this peak value. ¿ 1999 American Geophysical Union