Growth and reproduction are 2 economically important traits in the poultry industry. Janus kinase 2 (JAK) participates in the JAK2/signal transducer and activator of transcription 5 growth hormone signaling pathway, which plays important roles in the processes of growth and reproduction. The present study was designed to investigate the association of JAK2 SNP and haplotypes with growth as well as with reproductive traits in chickens. Fourteen JAK2 SNP were identified by pooled DNA sequencing, and 5 of these were genotyped for 768 Beijing You hens by using a matrix-assisted laser desorption/ionization-time of flight mass spectrometry assay. For 5 growth traits, BW at 17 wk of age was significantly associated with JAK2 C28109928T and A28135099G (P < 0.05). The 2 SNP were strongly related to BW at first egg, egg weight at first egg, and egg weight at 36 wk of age (P < 0.05). The SNP JAK2 C28122751T was found to be associated with BW at first egg and egg weight at 36 wk of age (P = 0.041 and P = 0.046, respectively), whereas JAK2 G28132240C was related to egg number at 40 wk of age (P < 0.01). Further haplotype analyses showed that 4 haplotypes checked in the population had no distinct influence on growth traits but were associated with 7 reproductive traits, namely, age at first egg; BW at first egg; egg weight at first egg; egg weight at 36 wk of age; and egg numbers at 32, 36, and 40 wk of age (P < 0.05). The results indicated that the JAK2 polymorphisms could be potential molecular markers to improve laying performance and growth traits in chickens.