"She looks fantastic. She seems to be terrific," State Department spokesperson Victoria Nuland said after Clinton resumed her work at Foggy Bottom headquarters of the State Department and held meetings with her top officials.
However, at the advice of her doctors, she would not be travelling abroad, Nuland said.
Clinton was away from the State Department for about a month now because of stomach infection she developed during her European trip in early December. She was later admitted to the hospital towards the end of the year after doctor's detected blood clot in her head.
Doctors have now declared her fully recovered.
"Judging by the woman we saw this morning and the workload that she's got, she seems to be fully recovered," the spokeswoman said in response to a question.
Wearing a brilliant pink jacket, Clinton arrived at the State Department early in the morning and then went straight for her meeting with top State Department officials.
"When she walked in the room, she had a standing ovation from 75 people assembled and then Deputy Secretary (Thomas) Nides presented her with a gift from all of us in a big box," Nuland said.
"First of all he said, 'As you know, Washington is a contact sport.' And (then) she opened the box. Inside was a football helmet with the State Department seal, lots of good padding and also a football jersey that said Clinton on the back and on the front it says number 112, which symbolises the number of countries that she's visited as Secretary of State," she said.
"She (Clinton) loved it. She thought it was cool. But then, being Hillary Clinton, she wanted to get right to business. So we do what we always do in that meeting, went around the room, and she heard from everybody what they're working on and what's coming forward," Nuland said.