Since determination of factors influencieng childbearing delay can provide convenient approaches to prevent fertility decline, nowadays studying this issue is an important issue for demographers and it is also emphasized by planners and politicians. The aim of this study is to evaluate factors influencing first birth interval among 458, young Iranian married women in Tehran province. In this cross sectional study, stratified random sampling was used to collect data of a structured questioner in 2017. Women’s first birth interval was compared in confronting some demographic, socioeconomic and attitudinal factors by Kaplan-Meier estimates and Log-Rank test as non-parametric survival analysis tools. The mean of women’s first birth interval was 3.33±2.67 years with a median of 3.00 years. Kaplan-Meier estimates were significantly different between levels of women’s and their husband’s educational level, activity, and post materialism factor (p-value<0.05). Women with university education and who had husbands with university educational level had the largest first birth interval among all other educational levels. Employed women had longer first birth interval than unemployed ones. Women lived with employed husband had shorter first birth interval. High post materialism women had the largest first birth interval. Manuscript profile