Introduction: Given the current concerns about population decline and the prevalence of single-child families, as well as risky behaviors which are increasing in the community, there is a need to provide backgrounds for more information regarding the characteristics of single child and factors affecting the risk-taking of adolescents in these families to modify the risk factors of these in adolescents. Methods: This is a descriptive, analytical study. The sample was single-child adolescents and their parents conducted in the census method. The data collection tools were demographics questionnaires, Iranian adolescents risk-taking, and Baumrind parenting style inventory completed by the participants in health centers of Qazvin, Iran, in 2017–2018. The SPSS software version 24 as well as step-wise multiple linear regression model were used to analyze the data. Results: One hundred and seventeen adolescents aged 12–19 years participated in this study. About 79% of mothers and 69.3% of fathers had high education. Most of the mothers were homemakers (62.9%) and fathers were employees (76.9%). The regression model demonstrated that emotional and social supports reduce risk-taking. If a decision-maker or supervisor for a teenager is someone other than parents, moreover, when the number of meals served by parents is less than twice a day and lack of leisure-time increase the risky behaviors (adjusted R2 = 0.66, P = 0.003). Conclusion: Although many factors affect the risk-taking of adolescents in single-child families, parents can reduce their adolescents' risk-taking by increasing their social and emotional supports, planning for spending more time, and allowing them to participate in family decision-making process.