Accelerated aging at the elevated temperatures was performed, and degradation phenomena were investigated for the high radiance InGaAsP/InP LEDs emitting at the 1.2-1.3µm region. During aging, some of the samples showed dark structures such as DSDs and/or DLDs in the emitting region. DSDs are found to be due to the precipitates. The time required for the appearance of these defects(tDS) was given as functions of the current density(J) and the temperature(T), i.e.,t_{DS} \propto J^{-2} \cdot \exp(1.2eV/kT). Using LEDs without dark structures, accelerated aging at the elevated temperatures of 20-230°C was carried out for over 10,000 hours. The activation energy of homogeneous degradation was obtained to be 0.9-1.0eV. From the results of aging, the extrapolated half-life in excess of 5 × 109hours is estimated at room temperature operation, and these InGaAsP/ InP LEDs are very promising as a source in practical fiber-optical communication systems.