Background : Tuberculosis (TB) remains a major global public health issue. Thailand was classified by World Health Organization (WHO) as one of the fourteen countries with the highest burden of TB, multidrug resistant TB (MDR-TB) and TB/HIV coinfection. Addressing latent TB infection (LTBI) is one of the key factors to achieve TB elimination by 2035. LTBI treatment should be provided especially in high risk populations in order to reduce the risk of progression to active TB. It is a major challenge to control TB in correctional facilities (prisons). Many risk factors contribute to higher incidence of TB in prisons such as overcrowding, and limited access to health care services in prison settings. Inmates with LTBI may be at risk of developing active TB due to co-morbidities such as malnutrition and HIV infection. However, the data of LTBI in Thai prisoners is limited. The aims of this study were to determine the prevalence of LTBI and to evaluate the feasibility of providing the LTBI treatment for Thai prisoners at Klong Prem Central Prison in Bangkok, Thailand. Methods : A cross-sectional study was conducted in prisoners who agreed to participate by signing the informed consent. All participants who meet the eligibility criteria were interviewed using a questionnaire. LTBI was evaluated using Tuberculin skin test (TST). TST was read after 48-72 hours and indurations of ≥5 mm and ≥10 mm were considered positive among HIV-infected and HIV-uninfected participants, respectively. Serological testing for Anti-HIV, HBsAg, Anti-HCV and VDRL were performed for all participants. Additionally, interferon gamma release assay (IGRA) were tested among subgroup of 294 participants. Participants with positive TST or IGRA were considered as having LTBI. Isoniazid prophylaxis therapy (IPT) was offered to all LTBI participants. Initiation of IPT was dependent upon the readiness of the participants. The duration of IPT was 6 months for HIV-uninfected and 9 months for HIV -infected participants at a dosage of 300mg/day. Results : From August 2018 to November 2019, a total of 1,032 participants were enrolled. Thirty participants were excluded because of abnormal chest X-rays (n=25) and incomplete TST testing (n=5). Thus, 1,002 participants were included in the analysis. TST was positive in 359 (35.8%) participants and 181 out of 294 participants (61.6%) had positive IGRA, resulting in 466 (46.5%) participants that were considered to have LTBI. Interestingly, when we decreased the TST positive cut-off to ≥5 mm for all participants, the TST positivity increased to 70.3%. The sensitivity of TST positive at cut-off of ≥10 mm was 40.9% and at cut-off of ≥ 5 mm was 76.2% compared to IGRA. The risk factors associated with LTBI were history of incarceration (aOR 1.53, 95%CI, 1.16-2.01, p=0.002) and history of prior active TB (aOR 3.02, 95%CI, 1.74-5.24, p< 0.001). Majority of LTBI participants (n=383; 82.2%) agreed to take IPT. Among 356 (92.9%) participants completed treatment and 27 (7.1%) participants discontinued IPT due to the side effects of INH. Having HBV co-infection (aOR 4.92, 95%CI, 1.76-13.78, p= 0.002) and HCV co-infection (aOR 3.56, 95%CI, 1.12-10.59, p= 0.02) were associated with adverse events after IPT inititation. Aside from this, we found the prevalence of HIV, HBV, HCV and syphilis infections were high as 2.9%, 6.1%, 5.7% and 4.9%, respectively. Conclusion : In order to reduce TB incidence in Thailand, the assessment of tuberculosis in prisons is needed. This study showed a high prevalence of latent TB infection in prisons in Thailand. Almost half of the inmates have LTBI. Therefore, this population is at high risk for developing active tuberculosis. Moreover, the cut-off of TST ≥5 mm can increase the sensitivity of TST testing compared to IGRA. Our findings demonstrated that LTBI treatment in prison is feasible because 92.9% of them have completed treatment. However, after LTBI treatment, long-term follow-up for 3 years is warranted to determine the efficacy of IPT among prisoners. Given high prevalence of LTBI and high completion rate of IPT, LTBI treatment should be provided.