  We construct N=1 supersymmetric fractional branes on the Z_6' orientifold.
Intersecting stacks of such branes are needed to build a supersymmetric
standard model. If $a,b$ are the stacks that generate the SU(3)_c and SU(2)_L
gauge particles, then, in order to obtain just the chiral spectrum of the
(supersymmetric) standard model (with non-zero Yukawa couplings to the Higgs
mutiplets), it is necessary that the number of intersections a \cap b of the
stacks a and b, and the number of intersections a \cap b' of a with the
orientifold image b' of b satisfy (a \cap b,a \cap b')=(2,1) or (1,2). It is
also necessary that there is no matter in symmetric representations of either
gauge group. We have found a number of examples having these properties.
