Calorimetric studies have been performed on the Se$_{80-x}$ Te20 Pbx ($0 \leq x\leq 1.4$) samples at different heating rates (5−20 °C/min). The glass transition temperature Tg, the peak crystallization temperature Tp, and the melting temperature Tm are found to increase with increase in heating rate. The apparent activation energies for glass transition Et and for crystallization Ec have been calculated from the heating rate dependence of Tg and Tp respectively. The effect of Pb addition to the Se-Te matrix on the mechanism of crystal growth has been investigated. The glass transition temperature Tg and the peak crystallization temperature Tp initially decrease with small addition of Pb (x = 0.6) but increases with further addition of Pb (x > 0.6). The thermal stability and glass-forming tendency have also been studied.