The effect of annealing temperatures in the range of 348K-448K on the electrical resistivity of Sn-12wt%Sb lead free solder alloy was investigated using the four-probe method. The time exponent (n) calculated from the time dependence of the isothermal electric resistivity curves has an average value of 0.02, which may be attributed to the increased number of Sb-atoms in the matrix resulting from the dissolution of the β-phase. The calculated values of the activation energy for different annealing times are ranged from 0.003 to 0.006 eV. From the electron micrographs, micro-structure investigations are also presented and discussed.