Only a few families have been recognized in the 320 million year history of cockroaches. The 31st one, represented by monotypic Ol xiai sp.n. from the Myanmar amber is described here. It inhabited lowland forest near the shore. It possesses several unique morphological features including bipectinate antennae, round terminal palpomeres, sophisticated forewing shape with broken R and CuP forming a distinct unsclerotised area and with RS branched to both sides, and a huge foretibial spur. The new genus also displays several putatively apomorphic reductions (short antennae, rudimental femoral terminal spine, short pronotal chaetae, minor arolia, short palps). Synapomorphies with early ant-nest parasites (short antennae, dense pronotal setosity, irregular spacing of wing veins, indication of maculated colouration) suggest an origin from Blattidae or ancestral Mesoblattinidae during the Early Cretaceous. No plesiomorphies are apparent. An attached mite documents a phoresy on males. A syninclusion of a coccoid male is not ecologically informative at the given state of knowledge.