Idiosepius biserialis is a species of bobtail squid native to the southwestern Indian Ocean off southern Africa. Records of this species from the Andaman Sea probablyrefer to Idiosepius thailandicus. I. biserialis occurs in shallow waters inshore. Females grow to 10.5 mm in mantle length. The type specimen was collected off South Africa and is deposited at the South African Museum in Cape Town.