The heats of dissolution (ΔHd) of thiamine disulfide (TDS)-fatty acids (FA) complexes, (FA)6 (TDS), were measured at 310.15 K in ethanol using a calorimetric technique, where the FA are tetradecanoic acid (C14), pentadecanoic acid (C15), hexadecanoic acid (C16), heptadecanoic acid (C17) and octadecanoic acid (C18). The values of ΔHd were 432.8, 475.0, 493.3, 541.0 and 558.5 kJ mol-1 for (C14)6(TDS), (C15)6(TDS), (C16)6(TDS), (C16)6(TDS), (C17)6(TDS) and (C18)6(TDS), respectively. The values of ΔHd of (FA)6(TDS) increased by increasing the carbon numbers (n) of the constituent fatty acids. However, the plots of ΔHd of (FA)6(TDS) against n showed a zig-zag pattern which indicates an upward convex at an odd-numbered position, while the plots of ΔHd of FA against n indicate a single line pattern.The differences between ΔHd of (FA)6(TDS) and ΔHd of (6FA+TDS) were 23-37 kJ mol-1 for even-numbered FA and 33-41 kJ mol-1 for odd-numbered FA, indicating a stronger binding force for (FA)6(TDS) formed from odd-numbered FA than those formed from even-numbered FA. Furthermore, the estimated values for the binding force between FA and TDS are very small, leading to a conclusion that (FA)6(TDS) is a clathrate (or an inclusion compound) formed by van der Waals forces and hydrophobic interactions between FA and TDS.