The Barbier reaction has been utilized in the construction of CX (X = C, Si, B, N, etc.)bondsin organic chemistry for over a century. However, all reported strategies have been carried out in organic solvents or solvent‐free conditions involving solid–liquid or solid–solid phases, and gas‐phase Barbier reactions in one step are rare. In this work, a one‐step gas‐involved Barbier reaction for the synthesis of carboxylic acids under electromagnetic mill conditions is presented. This approach utilizes gas CO 2 at ambient pressure, which holds significant promise for isotope‐labeling chemistry. A variety of 13 C‐labeled carboxylic acids is synthesized efficiently using this method. This gas‐involved, liquid‐assisted grinding transformation could accelerate the advancement of this field.