Two women accused of murdering a Perth teenager will face a five-week trial in Western Australia's Supreme Court in October next year.

Jemma Victoria Lilley, 25, and Trudi Clare Lenon, 43, are alleged to have killed 18-year-old Aaron Pajich whose body was found under a concrete slab at a house in Broughton Way in Orelia in June 2015.

Mr Pajich who had Asperger's syndrome was last seen alive about 10 days earlier at a taxi rank at the Rockingham City shopping centre.

Today in the Supreme Court both Lilley and Lenon pleaded not guilty to the murder charge.

The women appeared separately via video link from Bandyup prison, with the court being told there are "some difficulties" between the two of them and they are being kept apart in jail.

They were both remanded in custody until they face court again in April next year.