We investigated the effect of acoustic phonon mediated damping on a telecommunication‐band excitonic Rabi oscillation in a single quantum dot (QD). The InAs/GaAs QDs were capped with an InGaAs strain‐reducing layer (SRL) to shift the exciton energy to the O‐band (the lowest dispersion band; 1.26‐1.36 mm). They were also embedded in an n ‐i ‐Schottky diode in order to prove the excitonic state in a single photo‐excited QD by photocurrent spectroscopy. The observed exciton linewidth increased linearly at the low temperature due to the exciton‐acoustic phonon coupling, and increased drastically above 40 K due to the nonlinear increment of the exciton‐LO phonon coupling. We successfully observed excitonic Rabi oscillation up to 40 K even though the acoustic phonon‐mediated damping increased with temperature. This result suggests that the telecommunication‐band QDs are useful in constructing the exciton‐based qubits under the influence of the coupling between excitons and acoustic‐phonons. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)