The two had been short-listed for the engineering, construction and commissioning of units 7 and 8 at the Kozloduy nuclear plant using Westinghouse’s AP 1000 technology.
In parliament 112 of 223 deputies present on Friday voted for Hyundai, Bulgaria's BTA news agency reported.
Bulgaria announced plans last year for two reactors at Kozloduy to add a combined 2,300 megawatts (MW) in capacity.
Unit 7 is due to be completed by 2033.
Kozloduy is Bulgaria's only nuclear power plant and dates back to the 1970s. It has two 1,000 MW Soviet-made reactors in operation, with four others having been closed by 2007.
