  We study the Lambda_c decay process to pi^+ and the meson-baryon final state
for the analysis of Lambda resonances. Considering the
Cabibbo-Kobayashi-Maskawa matrix, color suppression, diquark correlation and
the kinematical condition, we show that the final meson-baryon state should be
in a pure I=0 combination, when the meson-baryon invariant mass is small.
Because the I=1 contamination usually makes it difficult to analyze Lambda
resonances directly from experiments, the Lambda_c decay is an ideal process to
study Lambda resonances. Calculating the final state interaction by chiral
unitary approaches, we find that the piSigma invariant mass distributions have
the same peak structure in the all charge combination of the piSigma states
related to the higher pole of the two poles of the Lambda(1405). Furthermore,
we obtain a clear the Lambda(1670) peak structure in the KbarN and etaLambda
spectra.
