Introduction: The HIV prevalence in Nigeria has dropped significantly from 5.8% in 2001 to 1.4% in 2017. The HIV/AIDS epidemic in Nigeria has been fueled through heterosexual relationships. Sex workers are pivotal in the spread of the HIV virus, because they are susceptible to engage in risky sex for pecuniary reasons thereby increasing the pool of new HIV infections and by extension the national prevalence. Objective: This study was conducted to determine the knowledge of brothel-based female sex workers in Calabar metropolis, Cross River State, Nigeria about HIV and its prevention. Method: A cross-sectional study was conducted using an investigator administered questionnaire to elicit responses from 200 FSWs on their KAP about HIV and its prevention. The data was analysed using SPSS. Result: The knowledge of HIV and infection prevention practices was high among the respondents. They were abreast with the health and occupational hazard associated with their work. Majority (95%) of the respondents used condoms consistently with their clients to protect themselves from sexually transmitted infections. On their perceived risk of contracting HIV, 69.5% of the respondents said using condoms consistently with their clients guaranteed protection from contracting the virus; 15.0% had a contrary opinion. Conclusion: Consistent condom use by sex workers is critical in preventing the spread of HIV. The failure of 5.0% of the respondents to achieve consistent use of condoms with their clients is therefore worrisome. Capacity building to improve their condom-negotiation competencies is vital. All sex workers should be actively engaged in the response, and should have access to other preventive interventions like PrEP and PEP