The treatment of a rejection of tannery effluent was carried out on an organic nanofiltration membrane. The rejection was recovered from a leather manufacturing plant in the area of Algiers (Rouiba). The effluent of the bath of tanning and liming charged with chromium ions was the subject of this study. In the case of synthetic solutions, the experimental variations of the retention ranged from 94-99.9% depending on initial feed concentration. For the tanning bath, the results indicated that chromium retentions of 60 and 30% were observed respectively in acid and basic medium. In acid medium, the rejection of the bath of liming has generated a retention of 15%. The use of the model of Nakao et al. [1] based on the extended modified Nernst Planck equation enabled us to compare the theoretical retention of chromium ions with the experimental results and to calculate the membrane pore radius.