Alkylcarbonates of gamma-cyclodextrins were produced and their inclusion complexes with four poorly water-soluble drugs of different structures and solubilities were prepared. The alkylcarbonates and the alkylcarbonate drug complexes were characterized by DSC and XRPD; the physical mixtures were used as control. Solubility capacities were evaluated by phase solubility studies. The effect of alkyl chain length on the complexation and release behaviour was investigated as well. The XRPD patterns of alkylcarbonates showed that the derivatives lose the original crystallinity of gamma-cyclodextrins. The series of alkylcarbonates formed inclusion complexes with the drugs considered. Both XRPD and DSC analyses did not show neither the reflections of the crystalline structures nor the melting peaks of the drugs, respectively. These gamma-cyclodextrin derivatives can improve drug solubility and influence the drug release rates while the alkyl chain length may affect these properties.