Sexually Transmitted Infections (STIs) seriously affect population morbidity, mortality, and are a major public health problem worldwide. A cross-sectional study was conducted using the latest Demographic and Health Survey (DHS) data published between 2005 and 2022 for five Southeast Asian countries. The study's focus was on STI risk factors in the DHS of Timor-Leste, Philippines, Indonesia, Myanmar, and Cambodia. The study included 139,062 women of reproductive age, aged 15 to 49 years, who reported whether they had experienced an STI or its symptoms and had comprehensive information on the variables of interest, including socio-demographics, sexual behaviour and knowledge. The report shows that the prevalence of STIs or symptoms of STIs in 5 Southeast Asian (SEA) countries included in the study is 11.6%, with the highest prevalence found in Cambodia, and the lowest in Philippines. Women aged 15-24 years in Indonesia (17.08%) and Philippines (9.81%), had a higher risk of STIs than those aged 25-49 years. In most studied countries of SEA (Cambodia, Indonesia and Myanmar), poorer women had higher risk of STIs. Also, in most SEA countries (Cambodia, Indonesia, and the Philippines), knowledge of STIs was significantly associated with having an STI in women aged 15-49 years. Sexual behaviour factors showed that acceptance of beating a wife for refusing to have sex with her husband was associated with STIs in all countries except Myanmar. The association between women's characteristics in reproductive age including socio-demography, sexual knowledge and behaviour, and STIs or symptoms of STIs is varied in countries of SEA. STIs interventions can be tailored to the specific characteristics of women in each of the 5 countries of SEA.