Thermal behaviour of three cells at Egyptalum smelter was investigated during baking and start-up stages by inserting twenty thermocouples in the sidewall carbon blocks and ten thermocouples in the bottom carbon blocks. The baking time, final average cathode surface temperature and the relative standard deviation for the anodic current distribution for these cells were about 71 h, 852 °C and 10 %, respectively. The heat-up rate during baking stage and the cell stability during the early operation period were improved. Temperatures in the sidewall carbon blocks at the end the baking stage in the range between 71 and 113°C and gradually increased after start-up stage to the temperatures in the range between 558 and 737 °C. The start-up time for these cells was 52 h. Valuable thermal relations were obtained between the sidewall carbon blocks and the steel shell during the baking and start-up stages. The results showed the sidewall carbon temperatures were unaffected by small voltage changes during the baking stage, but it affected by small voltage changes during the start-up stage.