Police are investigating two separate house fires in Boulder and Coolgardie overnight.
About 2.30am Kalgoorlie firefighters were called to the Boulder property in Watts Close.
It took them about 45 minutes to control the blaze.
The brick and tile home was gutted by the fire.
Initial estimates put the damage at $300,000, a Fire and Emergency Services spokesman said.
Kalgoorlie detectives were last night investigating if the fire was deliberately lit.
It is understood four young men were seen leaving the scene of the fire.
Investigators are also examining a fire in Coolgardie, about 40km east of Kalgoorlie.
The fire at the Lindsay Street house started at 10pm and took firefighters two hours to bring under control.
The initial damage bill has been put at $80,000, a FESA spokesman said.