The Gd(III) coordination polymer [Gd(mes)(H₂O)₆]_n (1), where H₃mes stands for trimesic acid, was subjected to variable temperature/field magnetizations and heat capacity measurements. Analyses of the magnetic data revealed negligible magnetic interactions (zJ = −0.39 cm⁻¹) and the isothermal magnetic entropy change −ΔS_M = 36.0 J K⁻¹ kg⁻¹ at T = 2 K and B = 9 T. The evaluation of the heat capacity data resulted in a similar value of −ΔS_M = 34.8 J K⁻¹ kg⁻¹. Thus, compound 1 shows a quite large magnetocaloric effect among Gd(III)-based molecular coolants. Furthermore, the correlation of the magnetocaloric effect based on the mass concentration of Gd atoms (c_m(Gd)) was proposed as −ΔS_M = 39.5c_m(Gd)^0.364 taking into account the experimental data for more than thirty Gd(III) compounds.