In this assay, the evaluation of lipophilicity of four ACE-inhibitors and hydrochlorothiazide (HCTZ) with RP-TLC on cellulose layers was described using three binary solvent systems. The selected ACE inhibitors had sufficiently different structures which can indicate the method suitability for their lipophilicity evaluation as the model substances in comparison with HCTZ. In addition, the linear relationship between the RM-values and composition of mobile phases was established in the current study. From the regression data of the plots, the hydrophobicity parameters, R(0) M and m, were determined and C0 parameter was calculated. The correlations between the experimentally obtained hydrophobicity parameters and calculated log p values were studied. Furthermore, the obtained results were compared with those previously obtained on RP-18 modified silica gel. Very good correlation (r = 0.91; water-ethanol solvent system) between the chromatographically obtained hydrophobicity parameters and calculated log p values confirmed the selection of ACE inhibitors since lisinopril and quinapril were on the opposite sites of linear relationship. The results indicate that cellulose as an easily available sorbent can be successfully used for the lipophilicity investigation of examined substances with RP-TLC.