Subtiliolithus is an oogenus of fossil egg from the Nemegt Formation of Mongolia and the Ohyamashimo Formation of Japan.

The eggs are notable for a very thin eggshell.

They were originally classified as a distinct oofamily, Subtiliolithidae, but numerous similarities to Laevisoolithus have led to their reclassification as Laevisoolithid eggs.

A complete skeleton of Nanantius valifanovi was found associated with Subtiliolithus eggshells, indicating that the oogenus represents eggs of enantiornithine birds.

This egg fossil-related article is a stub.