<p>Sumatran laughingthrush (<i>Garrulax bicolor</i>) is a critically endangered passerine found only in the montane forests of Sumatra, Indonesia. This species remains the subject of only a modicum of scientific study, resulting in a paucity of fundamental knowledge of its natural history. In terms of its morphology, it is generally assumed to be sexually monomorphic. This study presents the first evidence of morphometric analysis in this species, evaluating five morphometric traits, including both wild-caught and captive-bred individuals (<i>n</i> = 49), to assess potential sexual dimorphism. Overall intersexual comparisons revealed a significant difference only in wing length, with males having 2.29% larger wings than females. Subsequent intersexual comparisons, categorised on the basis of groups’ origin, have revealed the same dominance in male wing length. Furthermore, detailed analyses suggest the potential impact of the captive environment on morphology. Captive-bred males exhibited a significantly shorter tarsus (<i>P</i> = 0.015) in comparison to their wild counterparts, while captive-bred females demonstrated a tendency (<i>P</i> = 0.055) to have larger culmen compared to captive-bred males. Despite the limitations imposed by the reduced sample size and the inclusion of captive-bred individuals who may have been influenced by domestication, the results provide initial quantitative evidence that challenges the assumption of sexual monomorphism in sumatran laughingthrush.</p>