The structure of eigenvalues of −y q x y λy, y 0 0, and y 1 m k 1 α k y η k , will be studied, where q ∈ L 1 0, 1 , R , α α k ∈ R m , and 0 < η 1 < · · · < η m < 1. Due to the nonsymmetry of the problem, this equation may admit complex eigenvalues. In this paper, a complete structure of all complex eigenvalues of this equation will be obtained. In particular, it is proved that this equation has always a sequence of real eigenvalues tending to ∞. Moreover, there exists some constant A q > 0 depending on q, such that when α satisfies α ≤ A q , all eigenvalues of this equation are necessarily real.