This paper investigated the thermal stability, tensile strength, and conductivity of deformation-processed Cu-14Fe in situ composites produced by thermo-mechanical processing. The thermal stability was analyzed using scanning electronic microscope and transmission electron microscope. The tensile strength and conductivity were evaluated using tensile-testing machine and micro-ohmmeter, respectively. The Fe fibers in the deformation-processed Cu-14Fe in situ composites undergo edge recession, longitudinal splitting, cylinderization, break-up, and spheroidization during the heat treatment. The Cu matrix experiences recovery, recrystallization, and precipitation phase transition. The tensile strength and conductivity first increase with increasing temperature of heat treatment, reach peak values at different temperatures, and then decrease at higher temperatures. The value of parameter Z of the in situ composite reaches the peak of 2.86 × 107 MPa2 pct IACS after isothermal heat treatment at 798 K (525 °C) for 1 hour. The obtained tensile strength and conductivity of the in situ composites are 907 MPa and 54.3 pct IACS; 868 MPa and 55.2 pct IACS; 810 MPa and 55.8 pct IACS; or 745 MPa and 57.4 pct IACS, at η = 7.8 after isochronal heat treatment for 1 hour.