Distribution of radioactivity in Hokutolite from Hokuto hot spring, Taiwan was examined by using an imaging analyzer. The cut surface of the Hokutolite along the growing direction was contacted with an imaging plate and a two-dimensional radioactive distribution including an underlying rock part was obtained. The image processed by a computer represents a heterogeneous distribution of radioactivity in Hokutolite due to incorporation of non-radioactive rocks and fine particles during its growing from hot spring water. Lower radioactivity had been expected for the part of Hokutolite near the underlying rock than that at the surface of the Hokutolite because of older age. However, we could not confirm such a decline of the radioactivity from the surface toward the deeper part of the Hokutolite.