As they have multiple sex partners, female sex workers are at a higher risk of sexually transmitted infections, including human immunodeficiency virus. Consistent and correct use of male condoms can reduce this risk. However, condom use among female sex workers is a complicated issue. Objectives: The purpose of this study was to determine the__ampersandsignnbsp; revalence of condom use and to evaluate the factors associated with its use among female sex workers in Karachi, Pakistan. Methodology: A mixed method study was conducted in Karachi, Pakistan. Quantitative data were collected from 200 female sex workers (FSWs) through a structured questionnaire, while Qualitative methods comprised40 in-depth interviews of every 5th female sex worker participating in the cross sectional survey, and Focus-group discussions. The information on socio-demographic characteristics, prevalence of condom use, factors associated with use of condoms, knowledge and awareness about STIs and HIV/AIDS was gathered. The data were analyzed using SPSS 18 and frequencies with percentages were calculated for all qualitative variables. Results: Average age of the participants was 27.9 __ampersandsignplusmn; 6.5 years. More than one third had no formal education with 85% reporting a monthly income of more than 8000 PKR[Mean; 16615 __ampersandsignplusmn; 10867 PKR]. Nearly half (52%) had spent 4 or fewer years in sex work. The average number of clients per day was 3 __ampersandsignplusmn; 1.5 per sex worker. FSWs attached to a brothel were 6 times more likely to use acondom in comparison with street based FSWs. Whereas, FSWs aged younger than 35 years were 2.7 times more likely to use a condom in comparison to older FSWs. Factors found to be associated with not using a condom included being in the sex work for more than 05 years, having sex with non-paying partners, alcohol use, non-availability of condoms, not being associated with a service delivery program and lack of knowledge that condoms can protect against HIV. Conclusion: The study revealed that the prevalence of condom use among female sex workers was low. FSW__ampersandsignrsquo;s lack of negotiating power for condom use was a major reason for its non-use. Other factors associated with not using condoms included not being attached to a brothel, being over 35 years old, more than 05 years in sex work, having sex with nonpaying partners, use of alcohol, unavailability of condoms, no exposure to a service delivery program and no knowledge about condom being protective against HIV.