Recently, the number of indirect female sex workers (FSWs) who work at bars/clubs and massage parlors is substantially increasing in Thailand; however, there are huge gaps in knowledge about HIV risk behaviors among indirect FSWs. This study aimed to describe and understand HIV risk behaviors among Thai FSWs in Bangkok in relation to sociocultural factors and work environment (e.g., bars/clubs, massage parlors, brothels, and street). Based on venue-based purposive sampling methods, Thai FSWs were recruited for qualitative interviews (n=50) and survey interviews (n=205). Based on mixed methods, the study revealed that HIV risk and substance use behaviors among FSWs significantly differed depending on work venues, although there were no significant differences between work venues on some key risk behaviors (e.g., inconsistent condom use with primary partners and customers; willingness to engage in unsafe sex with customers). A multiple linear regression analysis revealed that FSWs who had used illicit drugs, were young, had low levels of self-esteem, or reported STIs had frequently engaged in unprotected vaginal sex with customers. Also, FSWs who worked at bars/clubs, were young, had higher income, or reported STIs had frequently engaged in sex with customers under the influence of alcohol. Qualitative interviews illustrated FSWs' alcohol and drug use due to their stressful life (e.g., long working hours and a large number of customers) and easy access to alcohol and drugs. FSWs had shown inaccurate knowledge about HIV prevention methods and engaged in risky behaviors, such as washing vagina with water or toothpaste after having had sex with customers. The HIV prevention strategies in Thailand need to be re-structured through implementing evidence-based HIV prevention intervention programs for FSWs, which must address sociocultural factors (e.g., self-esteem) and alcohol and drug use specific to work venues.