Japan's jobless rate rose to a worse-than-expected 4.5 percent in October from 4.1 percent in the previous month, the government said on Tuesday.
In September, the government started including in its data three prefectures in the northeast of the country hardest hit by the March earthquake and tsunami, which left 20,000 people dead or missing.
The market had expected a slight rise in the overall unemployment rate to 4.2 percent for October.
The jobless rate for men stood at 4.8 percent while that for women was at 4.0 percent, the internal affairs ministry said.
In a separate report, the welfare ministry said that the ratio of job offers to job seekers was 0.67 in October, meaning there were 67 job offers to every 100 job hunters.
The ratio was unchanged from September as job offers relating to reconstruction in disaster-hit areas levelled off.