Monopalmitin films spread on aqueous solutions of sugars were studied as a function of temperature and subphase composition (sugar type and its concentration in the aqueous bulk phase). The addition of sugars expanded the structure of monopalmitin monolayers, especially if they had previously adopted a liquid-condensed structure. The extension of this expansion depends on the type of sugar added (glucose, fructose, and sucrose at 0.1 and 0.5 M), Thermodynamic parameters associated with transition from liquid-condensed to liquid-expanded structures are in concordance with the structural changes observed from rr-A isotherms, The experimental data taken from the isotherms were fitted to some representative state equations. For solid and liquid-condensed structures, a lineal regression was used, with higher slope for the more condensed monolayer structure. For liquid-expanded monolayers, models derived from the kinetic theory of two-dimensional gases fit the pi-A experimental data better.