This study was carried out through two growing seasons of 2018 and 2019 in a private vineyard orchard located at Aga district, Dakahlia Governorate, to study the effect of foliar spray with magnesium sulphate at 0.3%, salicylic acid at 500 ppm and potassium silicate at 2000 ppm individually or in combinations on yield, cluster and berry properties of Thompson Seedless grapes under clay soil conditions. Spraying grapevines especially with the treatment included the three materials (MgS+SA+KSi) for three times (at full bloom, two weeks after setting and 45 days after setting) recorded the highest values of vegetative parameters, yield and fruit physical and chemical properties, also the same treatment recorded the highest leaf and berry content of N, P, Ca and chlorophyll and carotenoids comparing with the untreated vines.