The National Republican Senatorial Committee raised $3.8 million in October, the most of any month this year, according to a committee spokesman.
NRSC spokesman Brad Dayspring said the total puts the GOP in a good spot to take back the majority in the upper chamber.
"Republicans are well positioned politically and financially to win the Senate majority. Democrats have major credibility and competence issues which will plague candidates throughout the year ahead," he said.
The NRSC has just over $5 million cash on hand and remains debt-free. Its Democratic counterpart hasn't released its September fundraising totals, but has consistently had more debt than the NRSC.
At the end of September, the Democratic Senatorial Campaign Committee had $7.5 million in debt and $10 million cash on hand. The NRSC had $3.4 million cash on hand at that same point.
By the end of September, the DSCC outraised the NRSC by $13 million this year, and has generally posted better monthly fundraising totals.
--This piece was updated at 3:40 p.m.