The 12d supersymmetry algebra is considered, and classification of BPS states
for some canonical form of second-rank central charge is given. It is shown,
that possible fractions of survived supersymmetry can be 1/16, 1/8, 3/16, 1/4,
5/16 and 1/2, the values 3/8, 7/16 cannot be achieved in this way. The
consideration of a special case of non-zero sixth-rank tensor charge also is
included.Comment: Minor changes.Accepted for publication in Mod.Phys.Lett.A.Latex fil