To provide a disposable toilet seat cover that keeps a toilet seat clean without soiling the lower surface of the toilet seat even when excrement splashes on the lower surface of the toilet seat after excretion, and also, prevents its functions from being easily impaired.

The disposable toilet seat cover 1 is configured to be mounted on a toilet seat 102 of a sitting toilet bowl 100. The disposable toilet seat cover includes a lower-surface cover having: a water-insoluble cover body formed to follow the planar shape of the toilet seat 102; and fixing means provided on one surface of the cover body and fixable to the lower surface of the toilet seat 102.