The Democratic Congressional Campaign Committee raised $7.3 million in May, according to a committee aide.
The haul brings the committee's cash on hand to $45.9 million as many of the cycle's most competitive House contests switch to general election mode.
More than $2.3 million came from online donations in May, according to the aide.
The National Republican Congressional Committee has yet to release its May fundraising numbers. At the end of April, the NRCC had $32.3 million in cash on hand.
These fundraising figures are due to the Federal Election Commission by the end of Friday.