A woman in her 50s was raped during a burglary at her home near Olney in the early hours of Saturday morning.
One man sexually assaulted the woman, while another man searched the property.
They both left the house after stealing an amount of cash, credit cards and jewellery.
Both men were white.
Investigating officer Det Con Kim McHugh from Milton Keynes Force CID said: “We are in the early stages of this investigation and are working to establish exactly what has happened here.
“The victim is in the care of specially trained officers and being fully supported.
“We have officers patrolling the areas and are doing everything to locate these offenders, so please speak to them if you have any concerns.
“If anyone has any information, I urge them to contact us immediately.”
Anyone with information can contact Thames Valley Police on the 24-hour Police Enquiry number 101.