Thirty percent Co-Sn substitution was observed in Tb 6 Co 2 Sn on the 2a crystallographic site. It results in the deviation from the 6:2:1 stoichiometry and formation of Tb 6 Co 2 . 3 5 Sn 0 . 6 5 . By means of magnetic and transport measurements it was found that this compound orders antiferromagnetically at T N =42 K, and then undergoes metamagnetic transition at μ 0 H=6.1 T. The anomalously high value of the effective moment points to the polarization of the 5d states of Tb. The magnetic and transport properties of Tb 6 Co 2 . 3 5 Sn 0 . 6 5 are qualitatively similar to those of Tb 3 Co.