Various techniques like spectroscopy (UV-visible absorption, fluorescence, H-1-NMR), dynamic light scattering (DLS), isothermal titration calorimetry (ITC), and volumetry (density and sound velocity) have been used to throw light on the interactional behaviour of vitamin B-1 i.e. thiamine hydrochloride (TH) with bovine serum albumin (BSA). The spectroscopic results revealed the preservation of tertiary structure of BSA after TH binding. The affinity value of the order of 104 M-1 has been deduced from both absorption and fluorescence titrations. Metal ion (Ca2+, Mg2+, K+, Mn2+, Na+, and Ni2+) effect on the interactional behaviour has also been monitored. The increase in the hydrodynamic size and decrease in the emission intensity through static quenching mechanism of BSA along with its non-specific nature of interactions with TH have been observed. The ionic interactions at lower TH concentrations and hydrophobic interactions at higher concentrations along with hydrational shell structural changes have been visualized from initial increase of both V and K-s values at lower while decrease at higher concentrations of TH. Calorimetric binding enthalpograms also show the initial exothermic binding process followed by endothermic. The involvement of ethylthiazolium part of TH in hydrophobic interactions whereas substituted pyrimidine ring part in hydrophilic interactions has been depicted from H-1-NMR measurements. (C) 2018 Elsevier Ltd.