We aimed to study the prevalence and determinants of non compliance to intensive phase anti tubercular treatment (ATT) in 111 HIV-TB coinfection patients, attending the APEX Referral Center for HIV/AIDS at Medical College, Kolkata with a specially-designed, semi-structured, pre-tested questionnaire. Compliance was defined as taking ≥95% of the total scheduled doses of anti-TB medicines during the intensive phase. Data was collected on socio-demographic parameters, disease information, patient's knowledge and barriers to treatment. The prevalence of non-compliance to ATT in HIV-TB coinfection patients was found to be 40.5% (95% C.I. = 30.5, 50.5). Multivariate logistic regression analysis showed that absence of proper counseling, lack of knowledge about correct route of TB transmission, visiting quacks during ATT and the urge to leave treatment once patient started feeling better were the significant determinants of non-compliance. "No Counseling" increased chances of non- compliance (adjusted O.R.) 47.12 times (95% C.I. = 7.99, 195.27); thereby being the single most influential variable towards the outcome. The present study finds an alarmingly high prevalence of non-compliance to ATT among HIV-TB coinfection patients. The results clearly indicate that adequate counseling about this coinfection and the importance of compliance, along with better patient-friendly orientation of DOTS programme is urgently needed. Collaborative TB-HIV activities are essential to ensure better ATT compliance in coinfection patients.