Aim: This study aims to evaluate clinically the effect of probiotic treatment on localized aggressive periodontitis patients. Subjects and methods: This study was designed as a randomized, controlled, split mouth clinical trial, carried out on localized aggressive periodontitis (LAP) which having almost two identical sites with clinical probing depth of ≥ 5 mm. Two contralateral sites were randomly divided into two groups, Group I: received conventional periodontal treatment, scaling and root planning combined with topical application of probiotic. Group II: received conventional periodontal treatment, scaling and root planning only. Patients were evaluated clinically using the following parameters: plaque index (PI), gingival index (GI), probing pocket depth (PPD) and clinical attachment level (CAL) and radiographically by radiographic bone density (pixel) at baseline, 3, 6, and 9 months. Results: Clinical and radiographic results of this study showed that: there were a significant reduction for assessed variables (Plaque Index, gingival index, probing pocket depth and clinical attachment level and significant increase in radiographic bone density in probiotic group compared to group II. Conclusion: Adjunctive use of topically applied probiotic appeared to be beneficial effect in localized aggressive periodontitis patients when compared with scaling and root planning alone.