The incident came on the 12th green of the Dubai Desert Classic on Sunday after Woods missed a putt for par.
The tournament director said Wood's spit is a breach of the European Tour's conduct.
"The Euro Tour is right - it was inconsiderate to spit like that and I know better," Woods said on Twitter. "Just wasn't thinking and want to say I'm sorry."
The tour's code of conduct states that when a player becomes a member, he "voluntarily submits himself to standards of behavior and ethical conduct beyond those required of ordinary golfers and members of the public."
The tour said it would not disclose the amount of the fine.
After trailing by one stroke going into the final round, Woods shot three over par, finishing tied for 20th place.
The Associated Press contributed to this report.