This paper aims to assess intention for having a single child in life course and its determinants among married men and women owned one child less than five years resided in Tehran city. A total of 920 men and women who had one child under five years old were selected among clients of government-based vaccination clinics in August 2011 in Tehran city using a stratified cluster sampling method and completed an anonymous questionnaire. The findings showed that 35.4 percent of men and women intended to have only a single child, while nearly 55.2 percent intend for two children, and only 9.3 percent intended for more than two children. Intention for a single child among men is 1.79 times that of women. In both men and women, with the increase of education, the score of individualism and lack of religious attachment, the intention for a single child increases significantly (OR=1.11, OR=1.25, & OR=2.23, respectively). While with the increase in concerns related to having a single child and social norms of the number of children, intention for a single child decreases significantly (OR=0.82, OR=0.75, respectively). However, unemployment among men increases intention for a single child about 7 times and among women, increase in individualism, intention for a single child increases significantly (OR=0.1.25). The findings of this study can be employed in population policies encouraging a second child using determinants of fertility intention which can be modified among men and women.