Surface tension measurement based on spontaneous capillary wave resonance in confined micrometer-sized liquid interfaces was demonstrated. A single-beam quasi-elastic laser scattering method was used to detect the resonance. Characteristic resonant modes were observed on a 44-μm-sized circular water surface. The frequencies of the peaks agreed well with those simulated by assuming planar resonance, and the relationship was further confirmed for triangular, square, and pentagonal water surfaces. Then, the applicability of the method was successfully demonstrated by surface tension measurements of aqueous solutions of sodium dodecyl sulfate. The sensitive detection of capillary resonance opens new possibilities for the chemical and biochemical analysis of liquid interfaces.