The ternary phase diagram for In-Ga-Sb has been determined experimentally and has been verified by calculation. Liquidus compositions are measured along several isotherms together with several solidus compositions on the pseudobinary phase diagram. For the calculation both liquid and solid are assumed to be nonideal. The activity coefficients are calculated using a model with temperature dependent interaction parameters. © 1971, The Electrochemical Society, Inc. All rights reserved.