Although many factors that generate changes in OVD of complete dentures are known, no information is available in the dental literature regarding the effect of using high expansion dental stone (type V) on changes in OVD. This study therefore investigated the effect of a high expansion dental stone on the changes in OVD of complete dentures. A compression moulding technique was used to process twenty sets of simulated upper and lower dentures. Sample was equally divided into two groups: group of type III dental stone (DST III), and group of type V dental stone (DST V). In DST III, the lower, middle and upper parts of flask were filled with type III dental stone; In DST V, the procedure was the same as DST III except for the middle layer that was made of type V high expansion dental stone. Changes in OVD were measured before and after denture processing. A Shapiro-Wilk Normality Test was applied, and then collected data were analysed with t-test statistics for statistically significant differences at the 95% confidence level. The two groups revealed small but statistically significant increase in OVD as a result of processing. The increase in OVD was significantly less in DST V than in DST III. The use of high expansion dental stone can be recommended as investing material to reduce the increase in OVD that occurs after processing complete dentures.