Hasbro Inc. posted an unexpected drop in fourth-quarter revenue as sales of Star Wars-related toys fell, slowing down after three straight years of new releases for the franchise.

The maker of Monopoly, Nerf guns and Disney Princess dolls posted a 2% sales decline during the key holiday quarter, well short of the company's forecast for sales growth of between 4% and 7%.

In addition to disappointing Star Wars sales, Chief Executive Brian Goldner blamed the shortfall on weakness in Europe and disruption from the Toys "R" Us Inc. bankruptcy.

Hasbro's Star Wars sales bump appears to be waning as the Walt Disney Co.-owned movie franchise has begun churning out new movies annually following a decadelong hiatus. On Tuesday, Disney announced plans for additional Star Wars films.

Mr. Goldner noted that the intergalactic series' return in 2015 came with pent-up demand and a long window ahead of the movie's release to sell toys. The latest installment, "The Last Jedi," however, didn't hit U.S. theaters until Dec. 15, and toys sales didn't pick up until then.

He dismissed suggestions that fans are tiring of Star Wars products and said the property should provide a large and stable source of annual revenue. "I don't see it as Star Wars fatigue," Mr. Goldner said. "I feel like there's great vitality in Star Wars."

Despite the fourth-quarter decline, Hasbro's revenue last year managed to top that of rival Mattel Inc. for the first time since 1993. For the full year, Hasbro's sale rose 4% to $5.21 billion, surpassing Mattel's $4.88 billion.

Hasbro has enjoyed a revenue surge in recent years, helped by the return of Star Wars movies, winning some key licensed properties from Mattel and growth among its own products like Nerf and Monopoly. That stretch has coincided with years of declining sales and a sputtering turnaround at Mattel, which owns Barbie, Hot Wheels and Fisher-Price.

With Mattel struggling, Hasbro last year approached its rival about a possible tie-up, and the two companies continue to be linked to possible merger talks.

Hasbro reported a fourth-quarter loss of $5.3 million, or 4 cents a share, compared with a profit of $192.7 million, or $1.52 a share, a year earlier. This year's results included a $296.5 million net charge stemming from changes in U.S. tax laws.

The Pawtucket, R.I., company reported revenue of $1.6 billion, below the $1.7 billion analysts polled by Thomson Reuters expected.

Write to Paul Ziobro at Paul.Ziobro@wsj.com and Cara Lombardo at cara.lombardo@wsj.com