United's first 787 flight took off at 9 a.m. PT Monday from Houston to Chicago.
United and airlines around the world grounded their Dreamliner fleets in January after incidents that included an emergency landing of one plane and a fire on another. The incidents never caused any serious injuries.
Since then, Boeing put a new battery system into the 50 787 jets already in service around the world. Federal authorities lifted the grounding order on April 19.
United is planning to use 787s on shorter domestic flights before resuming international flights on June 10 with new Denver-to-Tokyo service as well as temporary Houston-to-London flights. It's adding flights to Tokyo, Shanghai, and Lagos, Nigeria, in August.
United hopes to resume Dreamliner service at LAX sometime this week.
The Associated Press contributed to this report.