In case a hard steel wire (0.6%C, 1mm. dia.) was pickckled in 10% HCl or 10% H2SO4 solution, the effect by the addition of several organic inhibitors, i.e., thiourea, gelatine, glue, aniline, chiloramine-T and commercial inhibitors, in pickling acid were studied on the inhibition efficiency and pickling brittleness.The results were summarized as followed:(1) Generally, an increase of the concentration of the addition agent accompanied an increase of the inhibition efficiency to diminish the attack of pickling acid, until the max. efficiency was attained by a certain concentration which was assumed to correspond to the saturated adsorption of inhibitor on metal, and over that the efficiency was constant except a decrease was shown by thiourea on the contrary.(2) Increasing temperature of the pickling bath increased the efficiency until 50C, but over 60C it rather decreased.(3) The inhibition efficiency of any agent for the hard steel came out respectively 5-10% lower than for softsteel.(4) The effect on the pickling brittleness did not always correspond to the inhibitive effect, and especially thiourea showed quite an inverse relation.After all, the above mentioned agents were better suitable as inhibitor for the hard steel wire in the order: glue gelatine commercial inhibitors.