With slight improvement of ordinary Rossi circuit, a coincidence circuit of resolving time of 1.5×10-7 sec. has been built. Using this instrument, the annihilation radiations of small component β+-rays emitted by Zn65 have been investigated under various experimental conditions. The experiments demonstrate that the 0.21 Mev γ-rays found previously by some authors in Zn65 may be the backscattered γ-rays due to large component 1.12 Mev γ-rays of Zn65. Moreover, the coincidence rate of collimated annihilation radiations gives the percentage of β+-decay of Zn65 per total disintegration as (1.56 ±0.16)%.