During compression, powders fragment, plastically deform, and/or may behave both ways. Different profiles ofspecific surface area changes have been shown in several studies for many powders. In this study, the effect of alubricant on the specific surface area of a powder was studied during the consolidation process of the powder as anattempt to clarify the behavior of powders under compression. Changes in specific surface areas of Starch [Rice starch] , cellulose [Avicel [R] PH102] , spray dried lactose [Zeparox [R] , and dibasic calcium phosphate [Emcompress [R] werestudied using gas adsorption technique. Magnesium stearate was used as a lubricant. Specific surface area of plasticallydeforming materials; cellulose, and starch was clearly affected by the addition of lubricants. Spray dried lactosecombined both fragmenting and plastically deforming behavior in its consolidation under compression and its specificsurface area was slightly affected by the addition of lubricant. Specific surface area of fragmenting material; Dibasiccalcium phosphate was not affected by the addition of a lubricant