Activation of serotonin (5‐hydroxytryptamine; 5‐HT) receptors plays a role in adult neurogenesis and differentiation of neural progenitor cells (NPC). Herein, we examined the involvement of 5‐HT receptors in the differentiation of mouse induced pluripotent stem (iPS) cells into NPC. To induce embryoid body (EB) formation, mouse iPS cells were cultured on ultralow‐attachment dishes. All‐trans retinoic acid (ATRA; 1 μmol/L) and/or 5‐HT (0.03 or 0.1 μmol/L) was added to the EB cultures for 4 days and then EB plated on gelatin‐coated plates were cultured for 7 or 14 days. Immunofluorescence staining revealed that mouse iPS cells expressed both 5‐HT2A and 5‐HT4 receptors and, to a lesser extent, 5‐HT1A receptors. Treatment with 5‐HT significantly enhanced the ATRA‐induced expression of nestin, a specific marker for NPC, and phosphorylation of cAMP response element‐binding protein (CREB). Pretreatment of EB cultures with either 1 μmol/L GR113808 (a selective 5‐HT4 receptor antagonist) or 1 μmol/L H89 (a protein kinase (PKA) inhibitor) significantly inhibited these effects of 5‐HT. These findings suggest that stimulation of 5‐HT4 receptors may enhance ATRA‐induced neural differentiation of mouse iPS cells through activation of PKA and CREB.