Oxidative stress may play an important role in the onset and development of oral inflammatory and dental decay diseases. The aim of this study was to compare total antioxidant capacity (TAC) levels in the unstimulated whole saliva of children with severe early childhood caries (S-ECC) and caries-free children. In this case-control study, 80 children aged 3-5 years from nursery schools in Babol, northern Iran were the subjects of the study. The S-ECC group contained 40 children with dmfs ≥4 (age 3), ≥5 (age 4) or ≥6 (age 5) and the control group contained 40 caries-free children (dmfs = 0). Out of consideration for growth pattern and general health, the clinical examinations of the chosen children were conducted by a physician. These two groups were age and sex matched. TAC was measured by the FRAP (ferric-reducing antioxidant power) method and total protein in unstimulated whole saliva was evaluated spectrophotometrically. According to the normal distribution of data, statistical tests including the t test and Pearson's correlation test were used; p < 0.05 was considered significant in the difference between the two groups. TAC levels and salivary total protein increased in children with S-ECC compared with caries-free children (p = 0.025 and p = 0.033, respectively). Moreover, salivary TAC showed a significant positive correlation with total protein concentration and dmfs in the S-ECC group (p < 0.001, r = 0.685 and r = 0.902, respectively). The significant increment of salivary TAC in S-ECC may represent a compensatory mechanism against oxidative stress in S-ECC.