The platinum-selling rapper admitted Tuesday that he failed to pay taxes on more than $3 million in income earned between 2004 and 2006.
He entered his guilty plea in a federal courtroom in Newark.
As part of a plea agreement, the government has dismissed two counts against him for unpaid taxes on income earned in 2007 and 2008.
The 35-year-old Ja Rule is expected to be sentenced on the tax evasion charges in June. He also faces sentencing that month in New York on an attempted weapon possession charge that he pleaded guilty to in December. He has agreed to a two-year prison term in that case.
Ja Rule was nominated for a 2002 best rap album Grammy Award for "Pain is Love."