New attenuation relationships of vertical strong ground-motion parameters of rock sites in Western U.S. are presented in this paper, which are regressed using high-quality digital strong motion records from NGA (Next Generation Attenuation) database. The new attenuation relationships focus on vertical PGA (peak ground acceleration), PGV (peak ground velocity) and 5% damped spectral acceleration (period from 0.04 to 6.0s). Ratio of vertical to horizontal component of spectral acceleration is calculated with another attenuation relationship, which was regressed using the same regression procedure and strong-motion data, and characteristics of how V/H ratio varies with period, magnitude and distance are studied in this paper. The new vertical attenuation relationships are recommended to be used with surface wave magnitude ranged from 5.0 to 8.0, and epicenter distance ranged from 0 to 200km.