Mothers are directly responsible for the dental health of their offspring and can play an important role in preventing oral diseases in children. They clean teeth of their children, teach them proper hygiene and dietary habits, and organize professional dental care. The aim of this study was to investigate the relationship between oral health knowledge of mothers and dental caries in Tripoli, Libya. A cross sectional study was conducted on 392 mothers of 6 to 12 years old children who visited the three public health centers, and one of the biggest public health hospitals for regular check up or other health problem in Tripoli. A validated questionnaire was used to examine mother`s knowledge about oral health and dental examination was carried out to assess the their children's caries experience. DMFT was statistically significantly associated with the mother`s knowledge according to chi-square test. Approximately half of mother’s had poor knowledge (49.7%), (40.1%) had average knowledge and only (10.2%) had good knowledge about oral health The higher prevalence of DMFT score was observed among children with poor mother`s knowledge (36.4%), while the lowest prevalence was observed among prevalence of DMFT values amongst children with good mother`s knowledge (15.0%). The relationship was statistically significant (P-value= 0.031). In conclusions the prevalence of DMFT was affected by the level of mother`s knowledge, the children whose mothers with good level of knowledge had the lowest prevalence of DC, while the children whose mothers with poor level of knowledge had the highest.