Objectives: Total fertility rate (TFR) in Iran is declining to the lowest low level over the past 30 years. In order to increase the TFR, the influencing factors for willingness to have child should be identified. The aim of this study was to identify the factors that influence the willingness of Iranian men and women to have child. Materials and Methods: This cross-sectional study was conducted on married Iranian men and women through an online survey. A questionnaire consisting of demographic characteristics, including age of subject, age of spouse, duration of marriage, number of children, education level of subjects and his/her spouse, current pregnancy status of subject or spouse, contraception use and type of contraception, and a validated questionnaire to identify the factors affecting willingness to have child in 4 domains (inter family factors, social factors, medical and parental factors and emotional and child related factors) were filled by subjects. Results: A total of 731 subjects (23.1% male and 66.9% female) answered the online questions. Mean age of subjects was 31.80 ± 6.83 years. Willingness to have child was significantly related to spousal age difference (P=0.002, odds ratio [OR] =0.90), number of children (P<0.001, OR=0.21), being pregnant (P<0.001, OR=82.91), level of education in spouse (P=0.03, OR=2.18), inter family factors score (P<0.001, OR=1.14), social factors score (P<0.001, OR=0.87) and emotional and child related factors (P<0.001, OR=1.52). Conclusions: This study revealed that willingness to have child in Iranian men and women is mostly influenced by personal and spousal factors.