An adjustable toilet support designed to be installed under wall mounted toilets in order to increase their load bearing capacities is disclosed. The toilet support comprises a base which rests on the floor below the toilet, a sleeve surrounding an upper portion of the base, and a contact member that contacts the underside of the toilet bowl. The sleeve and swivel ball are height adjustable with respect to the base by means of a support rod connected to the contact member and threaded into a nut contained inside the base. The support rod has an upper ball that fits within a socket under the contact member. The contact member may be in the shape of a swivel ball having a generally spherical side surface that contacts and holds the upper rim of the sleeve. During installation, the toilet support is positioned under the toilet, and the base is rotated while the sleeve, contact member and support rod are held against rotation, which causes the contact member to rise and contact the toilet bowl.