This paper studies the influence of the informal institutional factor of regional intergenerational mob-山ty, on family involvement in firm management.The results show that, the higher level of the regional intergenerational mobility, the less family members of actual controllers are involved in the firm management. The mechanism analysis suggests that, a higher level of intergenerational mob山ty, via strengthening the general trust, weakening the limited trust, and enhancing the fairness perception of the actual controllers, inhibits their demand for family members in the firm management; meanwhile, regions with higher intergenerational mob山ty also have more efficient labor-resource allocation, leading to a higher market supply of manager candi-dates, The above two impacts may combine to lower the involvement of family members in local firms'man-agement. Further analysis shows that, on average, family involvement in the management helps ease the agen-cy cost. Nevertheless, such an effect does not exist in areas with low intergenerational mobility, which indi-rectly suggests the "irrational" choice in enterprises'management team caused by the stagnant intergeneration-al mob山ty. This paper introduces an informal institutional factor, intergenerational mobility, into the analysis of the cause of the family involvement in firm management, and provides evidence from a new perspective for further research in this field.