A radiation streaming analysis for the radial and tangential beam tubes of a 250-kW TRIGA reactor was performed using the MCNP-MCNP coupling method. The measurements of the neutron flux and dose rate in the beam tubes were also conducted using gold-aluminum foils and thermoluminescent dosimeters. When compared with the experimental results, the calculated thermal neutron flux reproduces the measurement well, i.e., within 2 to 90%. The calculated nonthermal neutron and gamma-ray dose rates show about the same distribution along the beam tube as the measurements. For the neutron dose rate, there is a big discrepancy between the calculation and the measurement for the radial beam tube but good agreement for the tangential tube. The calculational method using MCNP-MCNP coupling, which is used here, may well be applicable to analyzing the particle streaming phenomena in the beam tube of a research reactor. The beam characteristics of the radial and tangential tubes were investigated based on MCNP calculations. The thermal neutron fluxes are about the same in both beam tubes, but the ratios of the thermal-to-nonthermal neutron flux and the thermal neutron-to-gamma-ray flux in the tangential beam tube increase from only 12% and 18% higher at the nose to 2.4 times and 2.8 times higher at 130 cm from the nose, respectively, compared with those for the radial tube. Thus, the tangential beam tube gives a better neutron beam quality, i.e., the same thermal neutron flux and lower nonthermal neutron and gamma-ray fluxes at the tangential beam tube exit as compared with the radial one.