In this article, a number of new integral and series relations between Mathieu functions of the second kind by the Meixner-Schafke definition and Mathieu functions of the first kind are established. These relations permit us to evaluate Mathieu functions of the second kind and their derivatives at the points z = pi m/2, m = 0, +/- 1, .... Bilinear series expansions of plane waves in products of Mathieu functions of the first kind are also derived in a simple way.