Experimental investigation on natural convection in a two-dimensional open cavity was performed using laser-Doppler velocimetry. The cavity is rectangular with one vertical heated wall facing a vertical opening, and with the two horizontal walls insulated. Studies for an open shallow cavity with an aspect ratio of 0.143 and Rayleigh numbers ranging from 106 to 107 under the steady laminar conditions were carried out using water as the working fluid. Heat transfer was found to approach that for a vertical heated flat plate. The measured velocity and temperature profiles illustrate the effect of the open boundary which can be viewed as consisting of two parts: the outgoing hot fluid flow exhibiting strong characteristics of the cavity condition, and the incoming flow influenced by outside conditions.