"The operation, with the objective of a resection of the detected brain tumor, started at 9 a.m. and concluded without complications," a statement from Madrid's La Paz hospital said.
A resection refers to a procedure to remove as much of a brain tumor as possible before radio- or chemotherapy.
The statement added that Ballesteros was conscious, in a stable condition and had been transferred to intensive care.
The 51-year-old was taken to the hospital last week after suffering dizziness and a brief loss of consciousness. On Sunday the five times major winner said he had a brain tumor.
Wednesday's sports daily Marca reported that the operation lasted 12 hours but did not say if the tumor was malignant or benign.
Ballesteros's office in his native Santander declined to comment and the spokeswoman for his family was not immediately available.
Ballesteros is one of the most gifted and charismatic players to grace the game, known for conjuring flamboyant rescue shots that saved him from often wayward drives.
When he won the British Open in 1979, he was the youngest player to do so in the 20th century. He won the title again in 1984 and 1988 and twice captured the U.S. Masters.
