Mattel Inc., the world’s largest toymaker, said fourth-quarter profit rose 33 percent over the year-ago period, boosted by a tax gain and the biggest sales increase in two years.

El Segundo-based Mattel reported earnings of $284.3 million (68 cents per diluted share) for the fourth quarter ended Dec. 31, versus $213.9 million (49 cents) for the comparable quarter of 2003.

Sales climbed 6.3 percent to $1.85 billion from $1.74 billion in the year-ago quarter, helped by the decline of the dollar. Fourth-quarter gross sales increased 10 percent in the U.S. and were up 3 percent in international markets. Operating income for the quarter was up 3 percent at $314.0 million, due mainly to higher sales volume.

A tax benefit, obtained through a settlement with the IRS regarding the examination of the company’s federal income tax returns for the years 1998 through 2001, boosted profit by $65 million.

For the fourth quarter, worldwide gross sales for the Mattel Brands business unit, which includes Barbie and Hot Wheels, were $1.13 billion, a 5 percent increase over one year ago. U.S. Barbie sales rose 3 percent, compared with a 25 percent plunge in the year-earlier quarter.

“Despite a challenging retail environment, we finished the year with improved momentum,” said Robert A. Eckert, Mattel’s chairman and chief executive.

Shares of Mattel rose 6.2 percent to $19.50 in mid-afternoon trading.