Education-job mismatch is an indicator that describes the quality of an individual's occupational achievements, with socio-familial background being one of the most influential factors in attaining these achievements. In this study, we aim to identify the extent to which the educational level attained by parents influences the education-job mismatch of university graduates. The analysis, deploying binary logistic regression models, is based on the Spanish Survey on the Labor Insertion of University Graduates 2019, with more than 30,000 cases. Main results are that parents' educational level largely determines the education-job mismatch of university graduates, acting through the intergenerational transmission of opportunities. In this sense, variables such as the field of study or those related to educational investment while at university are highly influential. When we analyze the persistence of mismatch, the influence of these variables is more decisive, so it is considered that there is an indirect influence of social background on occupational attainment through the variables linked to it. Recommendations are made for educational administrations that should favor equal opportunity measures and enhance the effectiveness of educational guidance services.