The present disclosure relates to an ionization chamber with a built-in temperature sensor, which is especially adapted for devices, such as X-ray units, gamma irradiators and linear accelerators, whichever is used for performing radiation dose output measurement accordingly. In an embodiment, the ionization chamber comprises: a cavity, an inner electrode, a chamber wall, an outer electrode, a guard electrode and a calibrated temperature sensor for detecting real-time temperature inside the cavity of ionization chamber to be used in the correction process of radiation dose measurement signals. With the aforesaid device, not only the accuracy of measurement can be improved effectively, but also the time consumed in a radiation dose measurement period can be reduced greatly since it will no longer bear the disadvantage that the radiation dose measurement has to wait until the temperatures inside and outside the cavity of ionization chamber had reached a thermal equilibrium before the measurement.