Effects of hydrogen on electrical properties and annealing behavior of radiation defects in N- and P-type Sⁱ (H) irradiated by neutron have been studied by DLTS, IR absorption, resistivity and minority carrier lifetime measurements. In as-grown and neutron irradiated Sⁱ (H), some Sⁱ -H IR bands and hydrogen-related deep centers have been observed. Because of hydrogen in silicon, the production rates of radiation defects decreased, and the passivation action of hydrogen emerged unambiguously at 200°c annealing temperature or higher. These cause the differences of annealing behavior of the resistivity and lifetime between Sⁱ(H) and Sⁱ(A^r).