  We study constraints on f(R) dark energy models from solar system experiments
combined with experiments on the violation of equivalence principle. When the
mass of an equivalent scalar field degree of freedom is heavy in a region with
high density, a spherically symmetric body has a thin-shell so that an
effective coupling of the fifth force is suppressed through a chameleon
mechanism. We place experimental bounds on the cosmologically viable models
recently proposed in literature which have an asymptotic form f(R)=R-lambda R_c
[1-(R_c/R)^{2n}] in the regime R >> R_c. From the solar-system constraints on
the post-Newtonian parameter gamma, we derive the bound n>0.5, whereas the
constraints from the violations of weak and strong equivalence principles give
the bound n>0.9. This allows a possibility to find the deviation from the
LambdaCDM cosmological model. For the model f(R)=R-lambda R_c(R/R_c)^p with
0<p<1 the severest constraint is found to be p<10^{-10}, which shows that this
model is hardly distinguishable from the LambdaCDM cosmology.
