In this study surface finish and dimensional charactersitics of castings produced with gypsum bonded block investment moulds were investigated. Commercial and laboratory made gypsum bonded investment moulds were used for investment casting mould making. To compare the casting quality of the investment powders, wax patterns for surface roughness specimens and linear dimension measurement specimens were designed and produced with special geometry. Wax trees were assembled with these patterns, cylindrical stainless steel perforated flasks were settled around the trees and gypsum bonded investment slurries were filled into flasks. Conventional tin bronze was subsequently cast into these moulds by vacuum assisted casting process. Afterwards, surface roughnesses of specimens were measured and linear dimensions of wax patterns and cast specimens were compared to determine percantage of dimensional change.