The analytical solution of convective heat transfer from an isothermal complex surface in an unlimited space has been presented. The complex surface is represented by a horizontal ring of diameters D and d with hemispherical segment of diameter d in the centre. The shape of the complex surface was expressed by factor rho = d/D. The presented solution has been verified experimentally on a set-up of diameter of 0.4 m and height of 0.5 m with surfaces of constant external diameter D = 0.06 m and various shape factor rho = 0-round plate, 0.183, 0.233, 0.40, 0.483, 0.554, 0.650, 0.817 and 1.0-hemisphere. The tested fluid was glycerine. The comparison of theoretical and experimental results gives good agreement.