The adolescent is considered an active element in family purchases, with an important participation in the decision phase, especially for those purchases in which he/she is the primary user or consumer. However, in purchases such as breakfast cereals, adolescent participation needs a more comprehensive study. The adolescent' presents, in this category of products, generally, a higher involvement and knowledge than his parents, which is an important resource in his participation in those purchases. Literature has evidenced the existence of diverse cultural dimensions, namely individualism-collectivism and power distance. In addition, the family buying decisions is one of the most difficult consumer behavior subjects. Thus, adolescents have become an increasingly attractive segment for companies because they are considered an active element and have an influence on the family, and on the other, they constitute a very important future market. In these, the role of the adolescent is not properly' explained, having often been devalued. Furthermore, products for adolescents' use have not yet been adequately studied, particularly the breakfast cereals. The main purpose of this research is to examine the influences of the national cultural constructs of individualism-collectivism and power distance, and consumer socialization effects on adolescent's influence on breakfast cereals purchase decision. A survey was used via two self-administered questionnairestwo questionnaires: one aimed at adolescents and the other directed at mothers, in high schools in Lisbon district, Portugal. 3,600 questionnaires were delivered in classrooms during May 2018. Adolescents' students, aged 12 to 19 years, were instructed to fill their questionnaires in the classroom and to deliver the remaining 1,800 questionnaires to their mothers' and to return them, fully completed, some days later. This resulted in a total of 726 questionnaires by mothers and 726 by adolescents, with a total of 1,452 validated questionnaires. Results on logistic regression analysis point to distance to power,concept-oriented communication, television influence, and internet Influence as explanatory variables for breakfast cereals' purchase. It can also be found a significant similarity of perceptions between the mother and the adolescent with regard to the participation of adolescent on that purchase decision. However, it is also important to point out some differences between mother' and adolescent' perceptions, which resulted on considering differentvariables as explanation ones for each member view of adolescent' influence. The mother's and adolescent's perceptions of his influence on the purchase of cereals is very similar. From mother' and adolescents' perception, concept-oriented communication, television influence, and internet Influence as explanatory variables for that purchase' influence. So, those adolescents living with consensual parents being perceived as having more influence on family purchases than those with protective parents. More, adolescents havi...