The study was carried out to assess the factors associated with HIV seropositivity among female sex workers (FSWs) in Dimapur, Nagaland, a high HIV prevalence state of India. A total of 426 FSWs were recruited into the study using respondent driven sampling (RDS). Data on demographic characteristics, sexual and injecting risk behaviours were collected from them and were tested for HIV, Syphilis, Neisseria gonorrhoeae and Chlamydia trachomatis. RDS-weighted univariate and multivariate logistic regression analysis was performed to assess the factors associated with HIV seropositivity. Consistent condom use with regular and occasional sexual clients was 9% and 16.4%, respectively. About 25% of the participants ever used and 5.7% ever injected illicit drugs. RDS adjusted HIV prevalence was 11.6%. In the univariate analysis, factors associated with HIV were initiating sexual intercourse before the age of 15 years, ≥2 years duration of sex work, serving clients at lodge/hotel, positive test result for one or more sexually transmitted infections (STIs), lifetime history of injecting drug use, lifetime history of consuming illicit drugs, ever having exchanged sex for drugs, having sexual partners who engaged in risky injecting practices and having been widowed or divorced. In multivariate analysis, factors found to be independently associated with HIV included lifetime injecting drug use, initiating sexual intercourse before the age of 15 years, positive test result for one or more STIs and having been widowed. Injecting drug use was found to be most potent independent risk factor for HIV (OR: 3.17, CI: 1.02-9.89). Because of lower consistent condom use among them, FSWs may act as bridge for HIV transmission to general population from injecting drug users (IDU) through their sexual clients. The informations from this study may be useful for enriching the HIV preventions effort for FSWs in this region.