The main aim of the present study is to investigate the effect of second glass modifier Na2O on the crystallization kinetics and thermal stability of the mol% xNa(2)O:(50-x)Li2O:50P(2)O(5) glasses, where Li+ ions are progressively substituted with Na+ ions, using differential scanning calorimetry. The DSC studies showed the classical 'mixed alkali effect' on the glass transition temperature, with the T-g minima for the glass composition of [Na+/(Li++Na+)] = 0.5 i.e. x = 25 mol% The crystallization temperature decreases as Na+ ions completely replaces Li+ ions. The presence of small concentration of second alkali (either the guest ion or host ion) tends to enhance the thermal stability, S, against devitrification as observed for 5 <= x <= 15 and 37.5 <= x <= 45. The 'mixed alkali effect' tends to thermally stabilize the intermediate compositions of mol% xNa(2)O:(50-x)Li2O:50P(2)O(5) as these compositions exhibited high S parameter, high activation energy for crystallization and low enthalpy of crystallization, Delta H-c. (C) 2013 Elsevier B.V. All rights reserved.