An organosilicone-treated silica obtained by treating(A) a silica powder having a specific surface area of at least 50 m.sup.2 /g with(B) a triorgano(1-alkoxyvinyloxy)silane having the formula (I): ##STR1## wherein R.sup.1 is a monovalent hydrocarbon group or an ether linkage-containing organic group, and R.sup.2 are each a substituted or unsubstituted monovalent hydrocarbon group or an ether linkage-containing organic group. The invention also discloses an organopolysiloxane composition containing the organosilicone-treated silica and a process preparing the composition. The organosilicone-treated silica is of high quality, containing no substance with disagreeable smell or corrosiveness which has been by-produced heretofore. Hence, the composition containing the silica is free from pseudocrosslinking such as structuring or crepe hardening.