Background: Down syndrome is often found to have periodontal disease as a result of poor oral hygiene, accumulation of dental plaque, debris, and calculus. Down syndrome is often found to have problems with periodontal disease, especially gingivitis (47.2% of mild gingivitis, 40.8% of moderate gingivitis, and 8.6% of severe gingivitis). The severity of gingivitis is caused by the presence of plaque deposits, plaque growth is related to the quality and quantity of saliva. Purpose: the purpose of this study was to determine the relationship between salivary pH and plaque index as a risk factor for gingivitis in children with Down syndrome. Method: quantitative research with cross sectional research design. The sample in this study were children with down syndrome in SLB BC in Surabaya, with total 62 children with down syndrome. The sampling technique of this research is purposive sampling. Data analysis was performed using multiple linear regression test. Result: There is significant effect between the pH of saliva and plaque index on the gingival index in children with down syndrome, which is 0.000. Strong predictors that affect gingivitis in children with down syndrome are salivary pH and plaque index (R=0.604) Conclusion: the salivary pH value and plaque index have a significant effect on gingivitis in children with down syndrome.