Let
be a biharmonic hypersurface with constant scalar curvature in a space form
. We show that
has constant
mean curvature if
and
is
minimal if
,
provided that the number of distinct principal curvatures is no more
than 6. This partially confirms Chen’s conjecture and the generalized
Chen’s conjecture. As a consequence, we prove that there exist no proper
biharmonic hypersurfaces with constant scalar curvature in Euclidean space
or hyperbolic
space
for
.