  Strange tribaryons as nona-quark (9 quark) states is studied to describe the
S=-1 resonance S^0(3115) recently discovered in the reaction K- + ^4 He -> S^0
+ p. We have identified S^0(3115) as a member of the flavor 27-plet, in
particular, (F_{flavor},I_{isospin},J_{spin})=(27,1,1/2) or (27,1,3/2). The
color-magnetic interaction between quarks favors small multiplets in flavor and
spin, which leads to a natural explanation that I=1 is the lowest state among
the S=-1 tribaryons with J=1/2. Classification of the S^+ -state recently
reported as well as possible locations of other light strange tribaryons such
as (10*,0,3/2) with S=-1, (8,1/2,1/2) with S=-2 and (1,0,3/2) with S=-3 are
also discussed.
