Aspirin (acetylsalicylic acid, ASA) is one of the most widely used analgesics. Aspirin is poorly soluble in water and causes gastrointestinal (GI) irritation. The bioavailability of several kinds of drugs solely depends on their dissolution properties in biological systems. In this direction, the physicochemical property of aspirin with phosphoric acid as an excipient has been studied. The kinetic energy obtained from viscosity method indicates that drug-excipient interactions are predominant and kinetic energy decreases with increase in concentration of the excipient. To improve the solubility, hence the bioavailability and minimize the GI irritation, its complexes with H3PO4 (in 1:1 ratio) were prepared in 1:1 C2H5OH and water. Evaluation of solubility and drug excipient interaction was done using scanning electron microscopy (SEM), FTIR spectra, X-ray diffraction, differential scanning calorimetry (DSC) and in vitro dissolution study. Aspirin-H3PO4 complex were found to be having rough surface in SEM. DSC, thermograms, XRD and FTIR confirmed the formation of the complex. Dissolution and pharmacokinetic studies of the designed drug was found to be of subsistence importance of Aspirin-H3PO4 as a possible drug to improve bioavailability of the drug. It was concluded that the complex of aspirin in definite propotion by weight may be of potential use for improving the solubility of aspirin and hence its bioavailability.