Sixty-eight-year-old Dutch expat Hans Lehner, who shared an apartment with Pranee Srijaem, called police about 10am when he could not rouse her.
Khun Pranee, 39, complained of a stomach ache and was ill before turning in last night at their address in Nanai Road, Patong, Mr Lehner told police.
Paramedics from the Kusolharm Foundation Phuket and a doctor from Patong Hospital responded to the call, with police.
Mr Lehner had a different meal when the pair ate out last night.
He sat down to watch television while Khun Pranee, his girlfriend of about one year complained of a serious stomach ache, then went to bed.
Paramedics estimated she had been dead for about three hours.