Around 20 members of the Public and Commercial Services Union (PCS) formed a picket line at the National Museum of Scotland in Edinburgh this morning.
The industrial action at the visitor attraction in Chambers Street is part of a dispute over weekend allowances.
The union said staff appointed after January 2011 were denied enhanced payments for working at weekends.
The PCS said the strike had been a success and added that it hopes management will listen to its calls.
Branch secretary Robert Burns said: "We won the fight to reinstate weekend payments a number of years ago and we will do so again.
"Management may think this is a way to run a national institution, but we don't.
"It may be a long struggle but we will continue fighting until all our members get a decent wage for the work they do."
The museum normally opens from 12pm to 5pm on Boxing Day.
The museum said the closure was outwith its control and apologised for the inconvenience.
It is due to open normally tomorrow.