Numb, an endocytic adaptor protein, is essential for multiple biologic processes. We previously reported that the deletion of Numb and its homologue Numblike (collectively known as, Numb Family Proteins or NFPs) specifically in heart causes a variety of morphogenetic defects, however, the key downstream target or signaling pathway that is disrupted and is responsible for each defect in the knockout was not determined. In this study, we investigated the cellular and molecular mechanisms of the trabeculation defect in the NFPs knockout. We found that during trabecular initiation, the cellular and mitotic spindle orientations of cardiomyocytes in the knockouts were significantly different from the control, which was further confirmed by the sparse cell-labeling / confetti clonal analysis. We then determined that N-Cadherin, which is required for trabecular formation in previous studies, is significantly reduced in the NFPs knockout. Genetic and biochemical tools were applied to demonstrate that Numb functions upstream of N-Cadherin and modulates its protein level to regulate trabeculation. Using chicken N-Cadherin driven by the aMHC promoter in transgenic mice, we found that cardiomyocytes that express chicken N-Cadherin in the NFPs knockout hearts preferentially localized to trabeculae compared to cardiomyocytes that do not express chicken N-Cadherin, thus partially rescuing the trabeculation defect of the knockout. This suggests that NFPs regulate trabeculation via maintaining the N-Cadherin protein level. To determine the mechanism of how NFPs regulate N-Cadherin protein, we generated a mouse line in which the endocytic motifs of Numb are deleted, and found the N-Cadherin protein level was not changed, indicating that Numb does not regulate N-Cadherin through endocytosis. Instead, we found that Numb localizes to the recycling endosome and that less N-Cadherin was localized to the membrane in the knockout, suggesting that NFPs are required for N-Cadherin recycling to the membrane. In summary, NFPs regulate N-Cadherin recycling to the plasma membrane during trabecular morphogenesis, and NFP deletion reduces N-Cadherin protein level, resulting in the trabeculation defect.