["Family Process, Volume 65, Issue 3, September 2026. ", "\nABSTRACT\nParents play an important role in adolescents' gratitude development, yet little is known about whether and how fluctuations in parents' gratitude (i.e., gratitude lability) over time are associated with adolescents' socioemotional adjustment. Using three‐wave data spanning 16 months, this study examined the longitudinal associations between parents' gratitude lability and adolescents' socioemotional outcomes, including depressive symptoms, life satisfaction, and prosocial behaviors, in 537 Chinese parent–adolescent dyads (MChild age = 10.25 years, SD = 0.69; 57.3% girls). Adolescents' gratitude lability was tested as a possible explanatory mechanism, and adolescent gender was examined as a moderator. Results showed that parents' gratitude lability was positively associated with adolescents' gratitude lability across waves, which in turn was related to adolescents' depressive symptoms and prosocial behaviors. Furthermore, for girls, parents' gratitude lability was indirectly associated with adolescents' prosocial behaviors via adolescents' gratitude lability. However, for boys, this indirect effect was nonsignificant. These findings underscore the value of a dynamic perspective for understanding the intergenerational transmission of gratitude and its developmental correlates. Future intervention research may benefit from examining whether more consistent parental expressions of gratitude can support adolescents' stable gratitude development, well‐being, and prosociality.\n"]