Abstract Aim This study examines the relationship between social and emotional loneliness and informal caregiving, focusing on the moderating role of anxiety about ageing among older adults aged 60 years and over. Subject and methods Data were collected through telephone interviews with a stratified random sample of 2,753 adults aged 55 years and older residing in the Basque Country, Spain. The sampling strategy ensured adequate representation across gender, age groups (55–64, 65–79, and 80+), and geographical areas. Measures included social and emotional loneliness, informal caregiving status and frequency, and anxiety about ageing. Regression analyses assessed whether anxiety about ageing moderated the relationship between caregiving and loneliness. Results Informal caregiving was not directly associated with loneliness. However, the relationship differed by levels of anxiety about ageing and caregiving frequency. At high levels of anxiety, occasional caregiving was linked to lower social loneliness, while frequent caregiving was associated with higher social loneliness. Conversely, at moderate levels of anxiety, frequent caregiving was negatively associated with emotional loneliness. These findings suggest that psychological factors influence how caregiving relates to loneliness. Conclusion Anxiety about ageing moderates the relationship between informal caregiving and loneliness among older adults. Public health interventions aiming to reduce loneliness among older adults should consider both anxiety about ageing and caregiving frequency, tailoring support strategies to the psychological and social needs of caregivers.