Background: Similar to the general public, mental health professionals sometimes also have negative attitudes towards individuals with mental illness; which could ultimately affect the quality of care received by the patients. This study aims to explore attitudes to mental illness among mental health professionals in Singapore; make comparisons with the general population; and investigate the significant correlates. Methods: A cross-sectional design was used. Eligible participants were recruited from the Institute of Mental Health, Singapore. Attitudes to mental illness among the mental health professionals were measured using an adapted 26-item Attitudes to Mental Illness questionnaire (AMI). An earlier study amongst the general population in Singapore had used the same tool; however, factor analysis suggested a 20-item, 4-factor structure (AMI-SG) was the best fit. This 4-factor structure was applied among the current sample of mental health professionals to allow comparisons between the professionals and the general population. Data were collected through an online survey tool ‘Questionpro’ from February to April 2016, and 379 participants were included in the current analysis. Attitudes to mental illness among these professionals were compared to those of the general population, which were captured as part of a national study conducted from March 2014 to April 2015. Results: The 20-item, 4-factor structure AMI-SG derived from the general population was applicable among the mental health professionals in Singapore. Compared to the general population, mental health professionals had significantly more positive attitudes to mental illness; however their scores on ‘social distancing’ did not differ from the general population. Indian ethnicity was negatively associated with ‘social distancing’ and ‘social restrictiveness’ among the professionals; while higher education was negatively related to ‘prejudice and misconception’. Compared to nurses, doctors showed significantly more positive attitudes on ‘social restrictiveness’ and ‘prejudice and misconception’. Having family or close friends diagnosed with mental illness was negatively associated with ‘social distancing’ among the professionals. Conclusion: The AMI-SG is an effective tool to measure attitudes to mental illness among mental health professionals in Singapore. Although the professionals had significantly more positive attitudes to mental illness than the general public in Singapore, their attitudes on ‘social distancing’ resembled closely that of the general public. Professionals tended to have more negative attitudes if they were nurses, less educated, and of Chinese ethnicity. More studies are needed to explore the underlying reasons for the differences and to generalize these findings among mental health professionals elsewhere.