Objectives <p>Alzheimer’s disease (AD) is the most common form of dementia in older adults with no cure. Early detection and intervention are critical for improving patient outcomes. However, behavioral intentions to seek early detection of AD (BI-SEDAD) remain low. Illness representations, referring to individuals’ beliefs about illness, may influence BI-SEDAD. This study aimed to investigate the associations between illness representations and BI-SEDAD among Chinese older adults, and potential sex differences in these associations.</p> Methods <p>A survey was conducted among 509 Chinese older adults. Participants completed the assessment of BI-SEDAD and illness representations of AD. Moderation analyses were conducted using SPSS PROCESS.</p> Results <p>Consequences (<i>β</i> = 0.26), timeline (<i>β</i> = 0.23), illness identity (<i>β</i> = 0.22), illness coherence (<i>β</i> = 0.21), illness concern (<i>β</i> = 0.22), and emotional representations (<i>β</i> = 0.24) were positively associated with BI-SEDAD, whereas treatment control was negatively associated (<i>β</i> = − 0.10). Moreover, sex significantly moderated the associations between BI-SEDAD and consequences (<i>β</i> = − 0.20), treatment control (<i>β</i> = 0.21), illness identity (<i>β</i> = − 0.17), illness coherence (<i>β</i> = − 0.25), and illness concern (<i>β</i> = − 0.26). Specifically, the associations between BI-SEDAD and consequences, illness identity, illness coherence, and illness concern were stronger in males than in females. The association between BI-SEDAD and treatment control was significant only in males.</p> Conclusions <p>Illness representations are important predictors of BI-SEDAD, with notable sex differences. Tailored interventions that address key beliefs and consider sex differences may promote early detection in older populations.</p>