The paper studies the periodic and anti-periodic eigenvalues of the one-dim
ensional p-Laplacian with a periodic potential. After a rotation number fun
ction p(lambda) has been introduced, it is proved that for any non-negative
integer n, the endpoints of the interval p(-1)(n/2) in R yield the corresp
onding periodic or anti-periodic eigenvalues, However, as in the Dirichlet
problem of the higher dimensional p-Laplacian, it remains open if these eig
envalues represent all periodic and anti-periodic eigenvalues. The result o
btained is a partial generalization of the spectrum theory of the one-dimen
sional Schrodinger operators with periodic potentials.