In an attempt to extend studies on the dehydration reactions of crystal hydrates from the inorganic to the organic field, the dehydration of l. asparagine monohydrate crystalline powders and single crystals was studied using isothermal and dynamic power compensation DSC as well as optical and FT-LR microscopies. The dehydration was strongly dependent upon the ageing of prepared crystals. Furthermore, crystals obtained by evaporation of solutions containing 30% methanol behaved differently.The kinetics of the overall dehydration results were independent of ageing and were characterised by obedience to the Avrami-Erofeev (n=3) law in isothermal runs at low and medium temperatures while, at the highest temperatures, first-order equations resulted in the best fit. In dynamic scans, order-of-reaction type laws gave the best fit and a dependence of the kinetic parameters on temperature gradient was ascertained.Optical microscopy revealed that the final textures of the surfaces of dehydrated crystals, depending on whether the reaction took place isothermally or not, differed. Moreover, non-isothermal runs performed under the microscope, at rates of temperature increase comparable with those used in DSC, revealed surface corrugation due to internal pressure generated by gaseous products as well as the presence of liquid phases.Micro-reflectance FT-IR spectra showed that dehydration started in the outer surface layers. These findings are typical of systems whose kinetics and mechanisms of decomposition are dominated by the properties of the outer boundaries of the crystals.The results are discussed in terms of a three-stage mechanism and a model accounting for these reactions is proposed. The relevant thermal and kinetic parameters are reported.