A method for synthesis of 6-hydroxy-1H-quinolin-2-one in ionic liquid was studied. The title compound was prepared from p-methoxyaniline via bromination, acylation and Heck reaction. The effects of reaction conditions on bromination and Heck reaction were investigated. p-Methoxyaniline was reacted with ionic liquid [bmim]Br3 to afford 2-bromo-4-methoxyaniline in 98.2% yield and 99.5% purity. N-(2-Bromo-4-methoxyphenyl)acrylamide was obtained by the acylation of 2-bromo-4-methoxyaniline with acryloyl chloride in 95.7% yield. The Heck reaction of N-(2-bromo-4-methoxyphenyl)acrylamide was effectively performed in the presence of ionic liquid [bmim]Br, Pd(OAc)2, K2CO3 and DPPP to afford 6-hydroxy-1H-quinolin-2-one in 91.5% yield. The new procedure for preparing 6-hydroxy-1H-quinolin-2-one has the advantages of good yield, simple operation and environmental benignity.