Tensile creep tests were conducted for an in situ single-crystal alumina/yttrium aluminum garnet (Al2O3/Y3Al5O12 (YAG)) binary system eutectic composite at temperatures between 1773 and 1873 K in air and in a moist environment having a water-vapor pressure range of 0.06-0.6 MPa, under a constant tensile stress range of 100-160 MPa. The Al2O3/YAG eutectic composite exhibited a stress exponent of 8-13, indicative of tensile creep behavior characterized by a dislocation back-stress mechanism. Water-vapor pressures less than or equal to 0.4 MPa led to a significant acceleration of creep rates as a result of enhanced dislocation mobility in the Al2O3 and YAG phases.