Background The elderly population in Malaysia are projected to reach almost one third of the total population by 2040. The absence of a National Dementia Strategy (NDS) in preparing the healthcare services for the ageing population is compounded by the lack of assessment of preparedness of future healthcare workers to manage complications related to ageing i.e., dementia. Studies in countries with NDS demonstrated lack of dementia knowledge among medical undergraduates. Hence, this study aimed to assess the knowledge on dementia among final year medical undergraduates in Malaysia and its associated factors, using the Dementia Knowledge Assessment Scale (DKAS). Methods This cross-sectional study, employed multistage sampling method to recruit final year medical undergraduates from eleven selected public and private medical institutions across Malaysia. Online self-administered measures were delivered to final year medical undergraduates through representatives of medical students’ society after approval from Deanery and institutional ethics board of participating universities. The measure collected demographic information, previous dementia exposure (i.e., formal or informal) and the 25-item Likert scale DKAS. Bivariate analysis and linear regression were conducted to confirm factors influencing dementia knowledge components. Results A total of 464 respondents from 7 universities participated in this study. Overall dementia knowledge among respondents with and without exposure, was low, with average score of 29.60 ± 6.97 and 28.22 ± 6.98, respectively. DKAS subscales analysis revealed respondents scored highest in care consideration subscale (9.49 ± 2.37) and lowest in communication and behaviour subscale (4.38 ± 2.39). However, only causes and characteristic subscale recorded significantly higher knowledge score among respondents with previous exposure (7.88 ± 2.58) (p =0.015). Higher knowledge of dementia was associated with previous formal dementia education (p=0.037) and informal occupational/working experience in caring for dementia patients (p = 0.001). Informal occupational/working experience (B = 4.141, 95% CI 1.748–6.535, p = 0.001) had greater effect than formal education (i.e. lectures/workshops) (B = 1.393, 95% CI 0.086–2.700, p = 0.037) to influence respondents’ knowledge on dementia. Conclusion Dementia knowledge among final year medical undergraduates is low. To improve dementia knowledge, Malaysian medical curriculum should be reviewed to incorporate formal education and informal occupational/working experience, as early as in undergraduate training to help prepare future healthcare providers to recognise dementia among ageing Malaysians.