Synsphyronus sertus is a species of pseudoscorpion in the Garypidae family.

It was described in 2021 by Australian arachnologists Karen Cullen and Mark Harvey.

The specific epithet sertus (Latin: 'join' or 'knit') refers to the fused metatarsi and tarsi.

Colouration is generally reddish-brown with paired darker patches.

The pseudoscorpions were found under shaded sandstone rocks in a south-facing gully.