Despite evidence of the impact of adult children's migration on left-behind older parents, the comparison of left-behind older parents’ mental health and psychological well-being between internal and international migration is limited. This article examines how the relationship between adult children's migration and parent's mental health differs according to the migrant's destination — only internal migration, only international migration, or hybrid migration (at least one child who migrated internally and at least one child who migrated internationally). Drawing on a 2019 cross-sectional population-based survey of 697 left-behind older adults (≥ 60 years) in Nepal, we assessed the mental health of older parents, using the 21-item Depression Anxiety Stress Scales and a range of socio-demographic, health, lifestyle, and child-related characteristics. Multilevel mixed-method linear regression was performed to examine the effect of adult children's migration on left-behind older parents’ depression, anxiety, and stress symptoms. Results showed that parents whose children had all migrated internationally were at higher risk of mental health problems, particularly anxiety and stress, compared to parents whose children had all migrated internally. Older parents from the hybrid group (having both internal and international migrant adult children) had higher levels of anxiety, compared to parents whose children had all migrated internally, with no significant difference in depression and stress symptoms. Further, mothers of internationally migrated children were at higher risk of mental health symptoms than fathers. Interventions aiming to improve left-behind older parents’ mental health and psychological well-being should specifically target parents whose children have migrated internationally.