The effects of soybean oil and cyclodextrin were studied on the quality characteristics and storage of frozen soy yogurt prepared from proteolytic soy protein isolate. The viscosity and overrun of frozen soy yogurt were improved by the addition of soybean oil and cyclodextrin. Upon the addition of cyclodextrin, there was a decrease in the peroxide value of yogurt with subsequent increase by the addition of soybean oil during frozen storage. During the process of storage, there was an increase in the acetone and diacetyl contents, but methanol, ethanol and butanol contents decreased. However, the value of hexanal content was not consistent in the obtained results. Sensory characteristics of frozen soy yogurt such as mouth feel, and overall quality were improved by the addition of cyclodextrin and remained the same frozen storage at $-20^{circ}C$ for 30 days.