The heats of dissolution (ΔHd) of fatty acids (FA)-nicotinamide (NAA) complexes, (FA)6(NAA)6, were measured at 310.15K in ethanol using a calorimetric technique, where the FA were tetradecanoic acid (C14), pentadecanoic acid (C15), hexadecanoic acid (C16), heptadecanoic acid (C17) and octadecanoic acid (C18). The values of ΔHd were 527.9, 574.6, 592.7, 640.1 and 656.6kJ mol-1 for (C14)6(NAA)6, (C15)6(NAA)6, (C16)6(NAA)6, (C17)6(NAA)6 and (C18)6(NAA)6, respectively. The values of ΔHd of (FA)6(NAA)6 increased by increasing the carbon numbers (n) of the constituent FA. However, the plots of ΔHd of (FA)6(NAA)6 against n showed a zig-zag pattern with an upward convex at an old-numbered position. This is the same tendency as observed for FA-thiamine disulfide (TDS) complexes, (FA)6(TDS).The differences between ΔHd of (FA)6(NAA)6 and ΔHd of (6FA+6NAA) were 30-48kJ mol-1 for even-numbered FA and 45-53kJ mol-1 for odd-numbered FA, indicating a stronger binding force for (FA)6(NAA)6 formed with odd-numbered FA than that formed with even-numbered FA. Furthermore, the estimated values of the binding force between FA and NAA are very small, leading to the conclusion that (FA)6(NAA)6 is an inclusion compound or a clathrate formed by van der Waals forces and hydrophobic interactions between FA and NAA.