The effects of substituting whey protein isolate (WPI) powder for rice flour during the preparation of paeksulgi (Korean rice cake) were evaluated by objective and subjective tests. Milk whey is drained from milk curd as a by-product of the cheese manufacturing process. Whey protein is known as a good nutritional source and a functional material for many processed foods. WPI contains more than 90% whey protein. The moisture content decreased gradually during storage and the decrease was less in control than WPI powder-substituted groups. The color lightness (L) decreased significantly with increasing WPI powder, wherease the redness (a) and yellowness (b) both increased. Texture analyses revealed that the hardness, chewiness, gumminess, adhesiveness and fracturability of paeksulgitended to increase in proportion to the amount of WPI powder added. Evaluation of the gelatinization of paeksulgi by amylographing revealed that the initial pasting temperature, peak viscosity, hot pasting viscosity and breakdown was lower in samples that contained WPI powder. However, the lowest setback value was observed in the control. The results of the sensory evaluation indicated that paeksulgi prepared with 2% WPI powder had the highest overall acceptability. Taken together, these results suggest that WPI paeksulgi containing 2% WPI powder has the best quality.