Alphas Branching Ratio in the Decay of Tb149

4.1-h ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tb}$ has been found to decay by $\alpha$ emission in (22.6±2.3)% of its disintegrations. This was determined by measurements of the $\alpha$ activity in a chemically and isotopically separated ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tb}$ sample and by determination of the amount of ${}_{}{}^{149}{}_{}{}^{}\mathrm{Gd}$ formed in this sample through electron-capture decay. Branching ratios of 0.475±0.055 and 0.104±0.013 were deduced for the 894- and 654-keV $\gamma$ rays of ${}_{}{}^{145}{}_{}{}^{}\mathrm{Eu}$ formed in the ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tb} \alpha$ decay.