This invention relates to organosiloxanes which have SiC-bonded ester groups and contain at least one unit of the general formula: ##EQU1## in which R represents the same or different monovalent hydrocarbon radicals having from 1 to 12 carbon atoms, which are free of aliphatic unsaturation and which may contain one ether oxygen atom; R' represents hydrogen or a methyl group (CH.sub.3) and a is 0, 1 or 2. These organosiloxanes can be prepared by hydrolyzing or co-hydrolyzing silanes of the general formula:ROOCCH.sub.2 CH(COOR)CH.sub.2 CHR'CH.sub.2 Si(CH.sub.3).sub.a X.sub.3-a,where R, R' and a are the same as above and X represents the same or different hydrolyzable atoms or groups. Also, they may be prepared by the addition of a diester of allyl succinic acid and/or methallyl succinic acid to an organosiloxane containing Si-bonded hydrogen. These new organosiloxanes may be used as lubricants for inorganic and organic fibers, metal surfaces and as hydraulic fluids.