Objectives: The aim of this study was determining the apical leakage after MTA and Portland cement (CP) usage as the root filling mateials both with two different lengths. Methods: The crowns of seventy single-root human extracted teeth were resected 10mm above the apex. Then the teeth were divided into four experimental groups(each with 15 teeth) and two control groups (positive control group with 2 and negative group with & teeth). Experimental teeth canals were cleaned & flared with the crown down technique using rotary files(Easy Race) and saline irrigation, and MAF#40. The experimental groups were filled as the following: Group A: Throughout the whole root length (10mm) with MTA, Group B: 5mm above the apex with MTA, Group C: Throughout the whole root length (10mm) with PC, Group D: 5mm above the apex with PC. Then, samples in B & D groups were rapped in moist cotton and were put in incubator (37 C & 100% moisture) for 24 hours. Next, the coronal parts of canals were filled with gutta-percha & AH26 sealer. After that, all the samples were rapped in moist cotton and were put in incubator for 72 hours. After the resection the end of all roots, the teeth were placed in 2% Methylene blue dye for 3 days. Finally, the samples were resected longitudinally and for determining dye penetration and apical seal were evaluated using a stereomicroscope (with 0.1 accurancy). The data were analysed using SPSS software (Kolmogrov Smirnov test and ANOVA0. Results: 1-Apical seal of PC was better than MTA regardless of the filling length significantly. 2-Apical seal of 5mm above the apex was better than of 10mm in both PC & MTA significantly. Conclusions: Portland cement can act as a suitable substitute of MTA. Filling length of 5mm above the apex is sufficient.