Periogen is a new caries activity test using real-time polymerase chain reaction. The aim of this study was to assess the validity of Periogen by evaluating the correlation with dmft, dmfts indices and comparing with Cariview and caries risk assessment tool (CAT).83 children under 6 participated in this study. Dmft, dmfts indices and CAT were collected through an examination of oral health status. Plaque samples for Periogen and Cariview were collected and manipulated according to the manufactures' instructions.The correlation coefficient of Periogen, Cariview and CAT with the dmfts index were 0.38, 0.56 and 0.66 in each (p < 0.01). The sensitivity of Periogen, Cariview and CAT were 43%, 76% and 95% and specificity were 80%, 72% and 74% respectively. Area under curve under the receiver operating characteristic curves in each method indicated 0.69, 0.81 and 0.85.CAT and Cariview were more effective in evaluation the risk of dental caries than Periogen so far. To be used Periogen clinically, more improvements for higher validity were needed. Abstract 354Corresponding author : Hyoseol Lee