<p>Out-of-school youth often face greater risks related to sexual and reproductive health than their in-school counterparts. Despite their vulnerability, limited research has been conducted on their levels of sexual knowledge, attitudes, behaviors, and access to sexual information. A cross-sectional online survey was conducted from December 1 to 12, 2022, using a convenience sample of out-of-school youth aged 15–24 from two suburban districts of Shanghai. Data were weighted using population census data for Shanghai’s suburban districts. Univariate and multivariate binary logistic regression analyses were used to explore predictors of sexual behavior. Unmarried out-of-school youth had inadequate sexual knowledge and limited access to sexual information, especially males. Around 15% reported having engaged in sexual intercourse. Among those who were sexually active, nearly half (47%) had multiple sexual partners, around 21% did not use any contraceptive method at first sex, and fewer than 10% reported an unintended pregnancy (8.8%) or an involuntary first sex (3.8%). Logistic regression indicated that youth who were male, internal migrants, employed, held more permissive attitudes toward sexual intercourse, and came from families with poor parental relationships were more likely to engage in sexual intercourse. School and family sexuality education were not associated with having had sexual intercourse. Out-of-school youth lack developmentally appropriate knowledge and skills required to fulfill their rights and make informed decisions regarding sexual behaviors and outcomes. There is an urgent need to develop comprehensive, developmentally appropriate sexuality education programs for young people in school, families, communities and other settings to promote empowerment, self-determination, and health of young people, particularly among those who are at high risk for negative outcomes.</p>