In this paper, we investigate the oscillation of a class of second-order linear impulsive differential equations of the form {(a(t)[x'(t) + lambda x(t)])' + p(t)x(t) = 0, t >= t(0),t not equal t(k), x(t(k)(+)) = b(k)x(t(k)(+)) = c(k)x'(t(k)), k = 1, 2, ... . By using the equivalence transformation and the associated Riccati techniques, some interesting results are obtained.