Lateral oblique and true lateral view of mandible are usually used for sialography of major salivary glands. Panoramic view has been recently introduced as a replacement procedure. Among these techniques, true lateral view of mandible with900 horizontal and vertical angles of projection has the least distrotion in images of salivary glands and duct patterns. But this technique because of super imposition of shadow of mandible of the opposite side, has lower diagnostic capability compared with the other two techniques. In the present study, probability of removing overlapping shadows and improving of diagnostic power of true lateral views with in vitro digital subtraction procedure has been evaluated. In this research a dry skull and 12 angio-catheter tube sets with 29 artificial filling defects measuring about 2 to 5 mm prepared in them was used. A total of seven radiologists and residents of medical and maxillo facial radiology evaluated digitized para-sialographic images before and after digital subtraction procedure. The results were analyzed with “Chi-square” and“Distribution-sensitivity frequency” tests. Data from analysis showed apparent improved diagnostic capability in true lateral view of mandible by using digital subtraction technique (P<0.05) while there was no statistically significant difference in lateral-oblique view of mandible (P>0.05). In conclusion, the present study showed if we replace lateral oblique view by true lateral of mandible to decrease distortion of sialography images, it is possible to improve image accuracy by digital subtraction technique.Key words: Digital subtraction, Sialography, True lateral of mandible, Lateral oblique of mandible