To investigate the toxic effects of dietary overload lithium on the adipogenesis in adipose tissue of chicken and the role of hypothalamic neuropeptide Y (NPY) in this process, one-day-old male chicks were fed with the basal diet added with 0 (control) or 100mg lithium/kg diet from lithium chloride (overload lithium) for 35days. Abdominal adipose tissue and hypothalamus were collected at day 6, 14, and 35. As a percentage of body weight, abdominal fat decreased (p<0.001) at day 6, 14, and 35, and feed intake and body weight gain decreased during day 7-14, and day 15-35 in overload lithium treated broilers as compared to control. Adipocyte diameter and DNA content in abdominal adipose tissue were significantly lower in overload-lithium treatment than control at day 35, although no significant differences were observed at day 6 and 14. Dietary overload lithium decreased (p<0.01) transcriptional expression of preadipocyte proliferation makers ki-67 (KI67), microtubule-associated protein homolog (TPX2), and topoisomerase 2-alpha (TOP2A), and preadipocyte differentiation transcriptional factors peroxisome proliferator-activated receptor-γ (PPARγ), and CCAAT/enhancer binding protein (C/EBP) α mRNA abundance in abdominal adipose tissue. In hypothalamus, dietary overload lithium influenced (p<0.001) NPY, and NPY receptor (NPYR) 6 mRNA abundance at day 6 and 14, but not at day 35. In conclusion, dietary overload lithium decreased the adipogenesis in abdominal adipose tissue of chicken, which was accompanied by depressing transcriptional expression of adipogenesis-associated factors. Hypothalamic NPY had a potential role in the adipogenesis in abdominal adipose tissue of broilers with a short-term overload lithium treatment.