Enhanced digital video microscopy is applied to study the equilibrium structure of a two-dimensional charged sulfate-polystyrene particle monolayer at decane/water interfaces. We are able to extract the pair interaction potential of these charged colloidal particles from Boltzmann equation by using the radial distribution function at very dilute conditions. The pair interaction potential of the two-dimensional colloidal particles is found to be a very long range repulsion and to decay with distance to the power of ¨C 3. When the surface density is increased, a sequential phase transition, pure liquid phase °ú liquid-hexatic-coexisting phase °ú pure hexatic phase °ú pure solid phase, is observed. It is obvious that the transition between liquid and hexatic phases is first order while the solid-hexatic phase transition is very likely to be second order. The temperature effect on this two-dimensional melting transition is explored by performing the experiments at three different temperatures. The charge effect on this two-dimensional melting transition is also examined by performing the experiments for three different surface charged particles. The Voronoi [Angew. Math. 134, 198 (1908)] construction is applied to analyze the defect structure in these two-dimensional particle monolayers.