Nickerson, 42, played 16 years as a linebacker in the NFL and was a five-time Pro Bowl performer. He had never coached at any level of the game before, and was working in broadcasting when Smith hired him after the 2006 season to oversee the linebacker position.
"Hardy did a good job for us," Smith told the team's Web site.
"He expressed how difficult this decision was, but he felt it was
best for him and his family at this time. I certainly understand
his decision and wish him and his family the best."
The spot opened up when former linebackers coach Bob Babich was promoted to defensive coordinator.
There was no immediate reason offered for Nickerson's resignation, and his future plans are unknown.
Nickerson's departure means that Chicago will have a fourth different linebackers coach in eight seasons in 2008.
Although weakside linebacker Lance Briggs earned a third consecutive Pro Bowl invitation in 2007, the performance of the Bears' linebackers slipped during the season, as did the play of the defense in general. Whoever replaces Nickerson for 2008 will likely be coaching a reconfigured unit, since Briggs is eligible for unrestricted free agency in the spring, and the club seems resigned to losing him.
During a standout playing career, Nickerson had stints with Pittsburgh (1987-92), Tampa Bay (1993-99), Jacksonville (2000-01) and Green Bay (2002).
Senior writer Len Pasquarelli covers the NFL for ESPN.com. The Associated Press contributed to this report.