Aggressive periodontitis is a destructive inflammatory condition affecting the investing and supporting tissues of the teeth. Adjunct use of antimicrobial agents was implemented for the treatment of the disease and also some antiseptic mouth wash like chlorhexidine digluconate 0.2%. With increase of bacterial resistant to antibiotics, now a day’s medicinal plants are used as antimicrobial against bacteria. Garlic (Allium sativum) has antimicrobial antifungal and antiviral against oral pathogens. Since Porphyromonas gingivalis, is one of the causative microorganisms of aggressive periodontitis among Sudanese patients, the aim of the present study was to study the effect of water garlic extract on Porphyromonas gingivalis compared to chlorhexidine digluconate 0.2%. Materials and methods: Fresh garlic cloves (100 g) were blended in 20 ml distilled water filtered using cotton wool and ultrafilterd under reduced pressure by using a Buchner funnel and a side armed flask. The final Concentration was 16.1% (v/w). Serial dilutions from 100%, 50%, 25%, to 12.5% and 10% of garlic were used in Muller Hinton agar media with Porphryromonas gingivalis suspension to determine the minimum inhibitory concentration, using chlorhexidine digluconate 0.2% as positive control and distilled water as negative control (in-vitro study). Zones of inhibitions were measured and averaged .the mean diameter of the zone of inhibition in mm was compared to the zone of inhibition of chlorhexidine using Pearson correlation test to identify if there is a statically difference between garlic extract and chlorhexidine digluconate 0.2%. Correlation is significant at the 0.01 and 0.05 level (2 tailed). Results: There was growth inhibition of Porphyromonas gingivalis by water garlic extract. Compared to chlorhexidine digluconate 0.2% there was no statistical significance difference between the means. **Correlation is significant at the 0.01 level (2 tailed). Pearson correlation of Garlic and chlorhexidine digluconate = 0.596; P-Value = 0.069. Conclusion: The present study indicates that garlic extract has the same effect of chlorhexidine digluconate 0.2% against Porphyromonas gingivalis, so it may have therapeutic value in prevention and treatment of aggressive periodontitis. So garlic extract can be used in well-designed clinical trial in form of mouth wash for prevention and treatment of aggressive periodontitis.