Red and white grape juices were treated with high hydrostatic pressure (HHP) at three different pressures, temperature and time values to investigate the effects of HHP on natural microflora and some quality attributes of the juices. Increased pressure, temperature and time showed significant effect on the microbial reduction and no microbial growth were observed in HHP-treated grape juices up to 90 days. HHP had little or no effect on pH and color of the juices. Although 5-hydroxymethylfurfural (HMF) formation was observed in heat pasteurized samples, no HMF was detected in HHP-treated juices. This study demonstrated that HHP could be used as an alternative to heat treatment.