The influence of distilled water and sulphuric acid solutions on the physicomechanical properties of neat and modified cement mortar has been investigated. The samples were immersed in distilled water, and different concentrations of sulphuric acid ranged from 5-15% by vol for immersion times from 1 to 120 days. The effect on the loss of weight, compressive strength, apparent porosity, water absorption, IR, and SEM were studied. The results indicate that the compressive strength and loss of weight decrease, whereas the apparent porosity and water absorption increase with immersion time and acid concentration. These are probably due to partial dissolution of the set cement. IR spectra and SEM studies showed significant changes in some absorption bands and the appearances of new voids of the neat and composite mortars after being immersed in H2SO4 solutions.