Activator protein-1 (AP-1) transcription factor is composed of JUN family proteins and FOS family proteins. Among Fos family genes, only Fosb gene produces two forms of mature transcripts, Fosb and ΔFosb mRNAs by alternative splicing. By alternative translation initiation, the former encodes full-length FOSB and vFOSB, while the latter encodes ΔFOSB and Δ2ΔFOSB both of which lack the C-terminal 101 amino acids of FOSB. We previously reported that Fosb-null mice show anxiety-like behavior, depressive-like behavior and adult-onset epilepsy, while Fosb^d/d mutant mice expressing only ΔFOSB and Δ2ΔFOSB do not show such abnormal behaviors. However, it is still unclear whether FOSB and/or vFOSB have some roles in these abnormal behaviors. To further understand how FOSB and/or ΔFOSB regulate such behaviors, we established Fosb^F/F mice expressing only full-length Fosb mRNA. By western blotting, we confirmed that only FOSB and vFOSB proteins, which are not detected in Fosb^d/d and Fosb-null mice, are detected in whole cell extracts prepared from Fosb^F/F mouse brains. We next performed a series of behavioral tests including open-field test, elevated plus maze test, repeated forced swim test and home-cage activity measurement. In elevated plus maze test, Fosb^F/F mice exhibited significantly decreased time spent on an open arm compared with wild-type littermates, as observed in Fosb-null mice. However, the immobility time during forced swim test and spontaneous locomotor activity were not changed compared with wild-type littermates. Moreover, Fosb^F/F mice did not exhibit adult-onset epilepsy. In summary, Fosb^F/F mice exhibited anxiety-like behavior, as seen in Fosb-null mice, but not depressive-like behavior nor adult-onset epilepsy. We thus concluded that FOSB and/or vFOSB are enough to suppress depressive-like behavior and adult-onset epilepsy, but not enough to suppress anxiety-like behavior.