The spectra of primary X-rays and secondary photons from shielding materials (lead, iron, heavy concrete, ordinary concrete and water) have been studied experimentally over the megavoltage region 4–30 MV, using NaI(Tl) scintillation spectrometers, from the point of view of radiation protection against a medical betatron. Spectral measurements were made of both photons transmitted through and scattered from the shielding materials. The measured pulse-height distributions were converted to photon spectra, using inverse response matrices of the crystals. Resultant spectra are tabulated in the unit of the relative photon number per unit energy interval. The average energy of primary and secondary photons has been calculated from the spectrum. Spectra experimentally determined are compared with theoretically calculated spectra.