The neutron diffraction technique was applied to measure strain distributions in a rebar in a reinforced concrete. At first, absorption coefficients of several kinds of concrete with different compounding ratios of water, cement, and aggregate were measured, and it was confirmed that the absorption coefficient of concrete was affected by the amounts of water and aggregate. In addition, it was also clarified by measuring strain change of the rebar under tensile loading that accuracy of the strain measurement in the rebar in the reinforced concrete was not affected by the neutron absorption by the concrete. Second, the size of the anchorage zone was evaluated by measuring strain distributions in the rebar under pull-out loading. The length of the anchorage zone measured by neutron diffraction was shorter than that measured by strain gauges. Moreover, detailed strain distributions in the rebar around cracks in the concrete were measured under tensile loading, and it was confirmed that the bond condition between rebar and concrete around cracks could be evaluated using the neutron diffraction technique.