Thestructural,electronic,andelasticpropertiesofZnSe1-xSxforthezincblendestructureshavebeenstudiedbyusingthedensityfunctionaltheory.Thecalculationswereperformedusingtheplanewavepseudopotentialmethod,asimplementedinQuantumESPRESSO.Theexchange-correlationpotentialistreatedwiththelocaldensityapproximationpz-LDAfortheseproperties.Moreover,LDA+Uapproximationisemployedtotreatthe"d"orbitalelectronsproperly.AcomparativestudyofthebandgapcalculatedwithinbothLDAandLDA+Uschemesispresented.Theanalysisofresultsshowconsiderableimprovementinthecalculationofbandgap.Theinclusionofcompositionaldisorderincreasesthevaluesofallelasticconstants.Inthisstudy,itisfoundthatelasticconstantsC11,C12,andC44aremainlyinfluencedbythecompositionaldisorder.Theobtainedresultsareingoodagreementwithliterature.