In Myanmar, Rifampicin resistant tuberculosis (RR-TB, a proxy for Multi-drug resistant TB) case detection is very low. Our study objectives were to assess the proportion of eligible TB patients who had not undergone RR-TB testing (Xpert-MTB/Rif tests) in Bago Region, Myanmar and to understand the reasons and solutions for non-testing. We conducted a mixed-methods study involving analysis of routinely collected programme data followed by key informant interviews (KIIs) with 32 health care providers. From October 2016 to March 2017, of the 2,331 eligible patients, 1,066 (46%) had not undergone Xpert-MTB/Rif testing. Patients from townships without Xpert-MTB/Rif testing facilities, new TB patients, patients whose HIV status was negative or unknown and extra pulmonary TB patients were less likely to undergo Xpert-MTB/Rif testing. From the health care providers' perspective, the most common reasons for non-testing were: (a) lack of awareness of the eligibility criteria; (b) difficulties in collecting sputum and transportation from eligible patients to the testing sites. We conclude that nearly half of eligible patients were not tested for RR-TB. Training of health care providers about the latest eligibility criteria and improvement in sputum collection and transportation systems particularly for townships without Xpert-MTB/Rif testing facilities are required to improve RR-TB testing.