A method is proposed for measuring either the solid-liquid contact angle or the liquid surface tension. The method applies the geometrical instability of a liquid meniscus, When a circular cylinder as a test solid is horizontally immersed into a liquid bath and lifted up gradually, a pair of two-dimensional meniscuses is formed under the side wall. At a certain critical height of the cylinder, the narrowest parts of the two meniscus curves contact each other, and the meniscus breaks down. Since the relation between the critical height H-Ber and the contact angle theta can be calculated theoretically, theta can be obtained by a simple measurement of H-Ber. It is possible to apply the same method for a plate used as a test solid. The liquid surface tension also can be measured by using a glass cylinder or plate to which most liquids attach at a = 0. The validity and usefulness of the method was experimentally confirmed for various solid and liquid samples.