His prized 1835 anvil was taken, along with two other anvils, during a break-in at his studio on Tuesday night.
A devastated Mr MacMillan is offering a reward for its return.
“I’ve been collecting for 30 years,” he said.
Get in front of tomorrow's news for FREE
Journalism for the curious Australian across politics, business, culture and opinion.
READ NOW“It’s not like I can just go out and buy another one.
“You get used to using certain tools and this was my favourite.
“I’ve achieved good work with it.”
Thieves also broke into his studio a few months ago and stole hammers and copper.
“I am gutted and in shock,” Mr MacMillan said.
He will be increasing security at his workshop.
Mr MacMillon has been a blacksmith for about 20 years and teaches at Dwellingup Forest Heritage Centre.
Examples of his sculpting work include the sculpture on the roundabout at Dolphin Quay and the pelican on Leslie Street.