We report the results of low-temperature magnetization and specific heat measurements Sr$_3$CoTa$_2$O$_9$ powder, in which Co$^{2+}$ ions with effective spin-1/2 form a uniform triangular lattice $ab$ plane. It was found that undergoes successive antiferromagnetic transitions at $T_{\rm N1}\,{=}\,0.97~{\rm K}$ N2}\,{=}\,0.79~{\rm zero magnetic field. As field increases, both N1}$ N2}$ decrease ...