Theridion albidorsum is a species of spider in the family Theridiidae. It is endemic to South Africa.
Theridion albidorsum is found only in South Africa. It is known from the Western Cape at Retreat Flats.
This species constructs three-dimensional webs in dark places. It has been sampled from the Fynbos biome at 37 m altitude.
Theridion albidorsum is known only from a juvenile specimen with a total length of 1.5 mm. The carapace is blackish brown with a central yellowish brown band. The abdomen is greyish brown.
Theridion albidorsum is listed as Data Deficient for taxonomic reasons by the South African National Biodiversity Institute. The species is known only from the type locality with a very small range. The status of the species remains obscure. More sampling is needed to collect the female and male and to determine the species range.
Theridion albidorsum was described by Embrik Strand in 1909 from Retreat Flats in the Western Cape. The species has not been revised and remains known only from juvenile specimens.