Abstract. We analyzed the recently published kHz quasi-period oscillaiton (QPO) data in the neutron star low-mass X-ray binaries (LMXBs), in order to investigate the different correlations of the twin-peak kHz QPOs in bright Z sources and in the less luminous Atoll sources. We find a power-law relation ν1∼νb2 between the upper and the lower kHz QPOs with different indices: b≃ 1.5 for the Atoll source 4U 1728-34 and b≃ 1.9 for the Z source Sco X-1. The implications of our results for the theoretical models for kHz QPOs are discussed.