This study examined the melting behavior and heat transfer characteristics of a water-insoluble material immersed in water. n-Hexadecane, popularly used as a phase change material, was selected as the water-insoluble material. A rectangular n-hexadecane solid was immersed in water. The n-hexadecane block was then vertically fixed onto the copper plate of the cooling wall. The flow structure of the free convection of water was visualized by mixing tracer particles with the water, and a laser sheet entered from the opposite side of the cooling wall as a light source. Its melting behavior and melting rate were then observed under various water temperatures in a test vessel. The local heat transfer coefficients of n-hexadecane were calculated from its melting rate and latent heat. In addition, the thickness of the melting liquid of n-hexadecane was calculated using a simple analysis model. As the experimental results, it flows upward along the n-hexadecane block, accumulates at the top of the solid as a droplet, and then flows upward vertically because the melting liquid of n-hexadecane does not diffuse in water. The calculated thickness of the melting liquid of n-hexadecane increases drastically near the lower end and increases almost monotonically and at a mild rate in other parts of the block. The analytical and experimental local heat transfer coefficients showed good agreement at low water temperatures. The calculated local heat transfer coefficients changed slightly, except for those at the top and low parts of the block. The local heat transfer coefficients increased in most locations as time elapsed in the experiment.