The stability constant of the binary 1:1 and 1:2 metal thymidine complexes have been determined from potentiometric titrations at 15°, 25°, 35° and 45°C and 0.1 M (KNO3) ionic strength. The metal ions studied are Cu(II), Ni(II), Co(II), Zn(II), Mg(II) and Ca(II). The stability constants of 1:2 metal thymidine are lower than the corresponding 1:1 metal thymidine system. The Δ log K for 1:2 metal thymidine are negative, as expected from statistical considerations. The enthalpy changes for 1:2 complex formation are less negative i.e. less exothermic than the corresponding 1:1 systems. The entropies are however more positive for 1:2 system. This is the normal trend for neutral ligands where the enthalpy is more favorable for 1:1 complexes (exothermic) as compared to 1:2 complexes.