The effect of some low molecular weight straight-chain diamines to inhibit the corrosion of SS type 304 in 1M HCl solution is examined by weight loss and galvanostatic polarization techniques. The inhibition efficiency increases with increasing the number of carbon atoms in the chain up to 8 carbons, but at higher than 8 carbon atoms (12 carbons) it decreases again. These diamine compounds act as mixed-type inhibitors, but the cathode is more polarized than the anode when an external current was applied. The corrosion rate in the presence of the investigated diamine compounds was found to increase with increasing the temperature and decrease with increasing the concentration of these compounds. Activation parameters for the corrosion of SS in 1M HCl were calculated and showed that corrosion was much reduced in the presence of inhibitors. The adsorption of these compounds on SS from 1M HCl solution obeys the Langmuir adsorption isotherm. The synergistic effect of KI on the inhibitive efficiency of the investigated diamine compounds was also studied.