A Rh(III)-catalyzed COOH-assisted C-H alkenylation of aromatic acids with unactivated alkenes at room temperature is described. Further, the highly challenging β-C-H olefination of acrylic acids with unactivated olefins was also demonstrated. In these reactions, ortho-alkenylated aromatic/vinylic acids were prepared in good to excellent yields. A possible reaction mechanism involving ortho C-H activation and a five-membered rhodacycle formation was proposed and supported by the deuterium-labeling studies and isolation of a key rhodacycle intermediate. Copyright © 2020 American Chemical Society.