The NASA astronaut entered the orbiting lab with Barry Wilmore at 1:15 am IST on June 7 in their third visit to space.
In a video released by NASA, Williams can be seen dancing as she enters the station's harmony module and greeted the other residents there.
Her joy shouldn't be a surprise as she reportedly cried when she had to leave the station during her last visit in 2012.
Williams and Wilmore are part of Boeing's Crew Flight Test - its debut mission with humans in collaboration with NASA.
Williams created history as the first woman to be part of a spacecraft's test mission.
The launch took place on June 5 from the Cape Canaveral Space Force Station after being scrubbed on May 7 and June 1.
Williams and Wilmore will stay aboard the station for a week after their arrival and test Starliner till the end.