Introduction and Aim: Preterm labor is a matter of concern in developed and developing nations, rural and urban areas as well. In this context a relatively cheaper biochemical marker in a specimen which can be easily collected from pregnant women will be beneficial in rural areas. Hence, in this context salivary estriol was selected for studying its diagnostic potential. Materials and Methods: A prospective study was conducted in two sittings (1st sitting at 26 to 29 weeks and 2nd after 2-4 weeks of gestation) among pregnant women (n= 206) who attended T.D. Medical College for antenatal check-up. The salivary samples were collected and estriol (E3) assayed by ELISA. The pregnant women were followed up till delivery to know the type, as term (n=194) or preterm (n=12). MedCalc was used for statistical analysis. Results: Reference interval of increase in salivary E3 over a period of 2 - 4 weeks in pregnant women during 26 – 32 gestational weeks who delivered at term by nonparametric method was 16 to 1468 pg/ml. Gestational period wise reference intervals of salivary estriol at 26- 28, 29 – 30 and 31 to 32 weeks were 74-3227, 119 -3422 and 203-4346 pg/ml respectively. There was a statistically significant difference in the increase in salivary estriol among different time intervals (p=0.001). Diagnostic cut off values of single measurements of salivary E3 and increase in salivary estriol between 2-4 weeks were 492, 561 and 159 pg/ml without acceptable diagnostic accuracy. Conclusion: Serial rise in salivary estriol at 2-4 weeks interval can be utilized but not a single measurement to monitor fetoplacental wellbeing. The high NPV of serial rise in salivary estriol (E3) suggests its usefulness to exclude chances for preterm labor.