Natural convective flows around an array of vertical heated plates were investigated experimentally. Main concerns were directed to the influences of plate numbers on the heat transfer characteristics of the plates. The both surfaces of the test plates were heated with constant and equal heat fluxes and their local heat transfer coefficients were measured. The results showed that the coefficients of the surfaces facing outward become higher than those facing inward of the array. The flow fields around the bottom of the plate array were visualized with smoke. The result showed that the ambient flow directs from the sides to the center of the array and enters the parallel channel obliquely. These flows cause the above difference in the coefficients. While the above difference gradually diminished in between the plates placed in the central part of the array, and their coefficients asymptote to those of the empirical equation that assumed a uniform velocity at the channel inlet.