The inhibition of corrosion of aluminium in HCl solution by some derivatives of thiosemicarbazones has been studied using weight loss and hydrogen evolution techniques. The thiosemicarbazone derivatives used are 2-acetyl pyridine-(4-phenylthiosemicarbazone) (PTSC), 2-acetyl pyridine-(4-phenyl-iso-methylthiosemicarbazone) (PIMTSC) and 2-acetyl pyridine-(4-phenyl-iso-ethylthiosemicarbazone) (PIETSC). The inhibition efficiency depended on the compounds concentration until at very low concentration studied where they reversed their functions and became accelerators. Kinetic treatment of the results gave a first order type of mechanism. The results reported in this paper elucidate the effects of inhibitor concentration, temperature and the molecular structure on the inhibition efficiency.