[en] The Monte-Carlo transport code, MCNP, has been applied in simulating organ dose for the MIRD-5 type adult phantom from isotropic semi-infinite photon sources in the air with source energies from 10 keV to 5 MeV. The minimum radius of source representing the semi-infinite source size is also determined. The obtained results of the organ dose were also compared with K. F. Eckerman et al. It is found that the present data are lower than those of K. F. Eckerman et al. However, the present data are lower than those of K. F. Eckerman et al in all energy regions. A possible reason is the difference in calculated by the Monte Carlo method, while those of K. F. Eckerman et al were calculated by the deterministic method. (author)