Objective To study the effects of gantry rotation time on image quality in 64-slice spiral CT. Methods Using the same CT technique and body mode as those used for 64-slice spiral CT, delta phantom was firstly layed on the isocenter, then scanned and reconstructed with SOMATOM Sensation 64-slice spiral CT. Slice sensitivity profile(SSP) was measured from which modulation transfer function (MTF) were got by Fourier transfer. The Catphan500 phantom was layed on the table, then scanned and reconstructed with SOMATOM Sensation 64-slice spiral CT. The maximum linepair and minimum size of the targets visualized. Results The MTF curve was nearly overlapped on 0.5 s and 1.0 s gantry rotation time, the values of 5% MTF were 11.3 LP/cm and 11.9 LP/cm. Their spatial resolution and low contrast resolution were completely identical.Conclusion The image quality is no distinction on 0.5 s group and 1.0 s group of gantry rotation time. In order to shorten the scan time and eliminate the breath defect, we suggest that the 0.5 s gantry rotation time be used routinely at body spiral scan mode.