Human-animal interactions are prevalent in institutions that display animals to the public. Visitors can affect the welfare of a wide range of captive species and stimulate the stress response, which influences energy metabolism. The koala evolved on a specific diet of extremely low energy content and is therefore likely susceptible to any effects from stress. However, the effects of visitors on captive koala behaviour and welfare are almost unknown. The effects of visitor number (Study1) and visitor noise (Study 2) were investigated in a population of 13 captive koalas. In Study 1, behavioural observations were conducted across eight days: four days of high visitor attendance and four days of low visitor attendance. Scan sampling was conducted every 2 min to record individual koala behaviour, position in enclosure, proximity to the boardwalk, and the number of nearby visitors within a 5 m radius on the boardwalk. In Study 2, the effect of visitor noise was investigated using audio recordings of visitor noise taken from the study site in three levels of treatment (No visitors, Quiet visitors and Loud visitors). Each koala was randomly allocated each noise treatment once daily over eight days and the presence or absence of vigilance behaviour was recorded. Study 1 demonstrated that an increase in the number of nearby visitors, but not total daily visitor number, resulted in increased time spent vigilant in the koalas. Study 2 showed that an increase in visitor noise treatment resulted in increased time spent vigilant in the koalas. These results show that koalas do respond behaviourally to visitors, supporting the value of behavioural observations as a monitoring tool to assess visitor-related disturbance in koalas. The welfare implications of these behavioural changes remain to be determined, as well as adequate management strategies to minimise negative visitor effects.