The complexation behavior of quinidine with four cyclodextrins (CDs)​, namely β-​cyclodextrin (β-​CD)​, hydroxypropyl-​β-​cyclodextrin (HP-​β-​CD)​, methyl-​β-​cyclodextrin (M-​β-​CD) and α-​cyclodextrin (α-​CD) was investigated for the purpose of improving the low aq. soly., stability and side effects of the drug.  The aq. soly. of quinidine was increased as a function of CD concn. generating linear A_L phase soly. profiles.  The interaction was quantified for quinidine-​CDs by detn. of the stability const. using the soly. method at various temps. and the thermodn. parameters were calcd.  The results revealed a very strong evidence for mol. interaction between the drug and HP-​β-​CD or M-​β-​CD, suggesting the formation of an equimolar complex.  The estd. enthalpies and entropies for the interaction of quinidine with CDs indicate that the interaction is exothermic.  The prepd. coevaporates were studied by x-​ray diffractometry, differential scanning calorimetry and IR spectroscopy, in order to investigate the possibility of complexation of the drug with CDs.  The relative potency of the CDs to enhance the dissoln. rate of quinidine was in the following order: M-​β-​CD ≥ HP-​β-​CD > α-​CD > β-​CD, which, generally fits the magnitude of the stability const. data of the complexes.  The dissoln. profiles of the drug, phys. mixts. of the drug with CDs, as well as, the prepd. complex show higher dissoln. rate of the complex compared with the drug alone or its phys. mixts.