The grey-sided bush warbler (Cettia brunnifrons) is a species of bush warbler (family Cettiidae). It was formerly included in the "Old World warbler" assemblage. It is found from northern Pakistan to central China. The phylogenetic relationships among the Cettia species are shown below, based on the data by the Cornell Lab of Ornithology. It split from the Cetti's warbler about 5 million years ago.
