A French scientist Sorel S.T., discovered magnesium oxysulphate cement (magnesia / Sorel?s Cement) in 1867. In this work the effect of formaldehyde as an additive is studied on some properties of Sorel?s cement. It is found that incorporation of formaldehyde in the matrix increases setting periods but does not contribute to the water tightness of the cement, though compressive strength of the product improves by its incorporation in small amount. Minor contractions in the linear beams are also noticed with passage of time.