Background: The present study evaluated the outcome of modified ridge split technique in posterior mandible in comparison to conventional technique Material and method: That was a randomized controlled clinical trial. The study population included 20 patients with edentulous posterior mandibular alveolar ridges (bucco-lingual width= 3-5mm). The sample was selected conveniently to fulfill a list of inclusion and exclusion criteria. Then the selected participants were allocated randomly into two equal groups each including 10 patients (study and control group). Both groups have undergone corticotomy procedure in the first stage using piezoelectrical surgical device. One month later, control group undergo conventional ridge split procedure with xenograft and collagen membrane. In study group, modified ridge split procedure was done with no bone graft. Bone chips harvested from ipsilateral retromolar area by trephine bur were crushed and used to maintain the space between buccal and lingual plated after splitting. Assessments included measurements of pain using Visual Analysis Score VAS (2nd, 7th, 14th day postoperative), edema using tape measuring method (2nd, 7th, 14th day postoperative), healing of the tissue (2nd, 7th, 14th day postoperative), and radiographic measurements of bucco-lingual crestal bone width at pre-operative, immediately post-operative, and 6 months post-operative (CBCT measurements). Result: The statistical analysis of measurements from both groups showed no significant difference between control and study groups regarding edema, pain, and tissue healing. Also buccolingual crestal bone width measured six months postoperative phase showed that there was a nonstatistically significant difference in the measurements of conventional group (μ= 6.02, SD = ±0.52) and the modified ridge split group (μ = 5.78, SD = ±0.90; p = 0.474). Conclusion: It can be concluded that narrow posterior mandible can be effectively expanded by modified ridge split technique. Moreover, this simple and predictable approach is not expensive because it omits the use of foreign materials and can be employed more often. Keywords: ridge split, modified ridge split, narrow mandible, piezosurgery, xenograft, collagen membrane.