This paper deals with the oscillation problems for nonlinear differential equations of the form $(r(t)
x'
^{p(t)-2}x')'+c(t)
x
^{\lambda-2}x=0$ involving $p(t)$-Laplacian. Leighton-Wintner type oscillation criterion is established without any conditions on the limit of $p(t)$. In addition, we discuss the nonexistence of singular solutions. Some examples are given to illustrate our results.