A regulatory filing Tuesday disclosed the San Francisco company lost nearly $65 million during the three months ending in September.
That's the largest quarterly setback that Twitter has suffered during the past three years. Twitter lost about $22 million at the same time last year.
In a development likely to hearten prospective investors, Twitter's revenue more than doubled from last year to nearly $169 million.
But the company's rising losses could dampen some of the enthusiasm for Twitter's initial public offering. The IPO is expected to be completed next month, though the company hasn't set a target date.
Twitter ended September with 232 million active users, up from 218 million in June.