High circular mobility creates vulnerability and elevates risk for sexually transmitted infections (STIs) including Human Immunodeficiency Virus (HIV). We aim to explore knowledge, perceptions of risk, and sexual behaviors in relation to STIs/HIV, in Mozambican women involved in an informal cross border trade (ICBT) and residing in South Mozambique. A cross-sectional quantitative study, in 200 women cross border traders (WICBT), affiliated to the Mukhero Association, using a structured, face-to-face questionnaire, was conducted. Descriptive statistics and Pearson’s Chi-square test were used. The median age of participants was 37.0 years (interquartile range (IQR): 31.0–43.0), 100% were literate, travelled on average six times a month. WICBT with a high education level were more likely to have awareness of Gonorrhea, Syphilis, and Candidiasis; to self-perceive being at risk of getting HIV, Syphilis, and Human Papilloma Virus (HPV); and to test for HIV and Syphilis. Those with a low education level were more likely to have misconceptions about HIV and ever have sex in exchange for money/goods/services. Married participants were more likely to know how to prevent HIV. Participants with a high income were more likely to know about HPV; to self-perceive being at risk of getting Syphilis; to point sex workers as being at higher risk of getting HPV; and to ever test for HIV. WICBT with a low income were more likely to have sex in exchange for money/goods/services. Low and inconsistent knowledge and misconceptions of STIs/HIV, high sexual risky behavior, low perception of risk of getting STIs/HIV among this neglected and key population suggests their increased vulnerability to the STIs/HIV.