The enthalpy of mixing for aqueous heavy rare alkali metal chloride (RbCl, CsCl) solutions with aqueous L-alanine solutions, as well as the dilution enthalpies of RbCl, CsCl, and L-alanine solutions in pure water have been measured at 5 K intervals from 298.15 K to 313.15 K. The transfer enthalpies of RbCl and CsCl from pure water to aqueous L-alanine solutions can be obtained from these data. The enthalpic pair interaction parameters of RbCl and CsCl with L-alanine in water are evaluated according to the McMillan-Mayer theory and discussed in terms of the electrostatic interaction, structure interaction, and Savage-wood group additivity mode.