This work deals with the impact of chloroform radiolysis on astatine chemistry. Astatine-211 is a promising radionuclide for the targeted alpha therapy of cancers. Yet, the production of 211 At based radiopharmaceuticals is often complicated by radiolysis due to its own decay, leading to solvent degradation and then impacting astatine chemical state and radiolabeling efficiency. A better understanding of the radiolysis phenomenon is thus necessary. Two experiments are performed: (1) pH measurement during the At extraction in chloroform medium, (2) pH determination calculated from the HCl chemical yield which is obtained during the radiolysis of chloroform medium by γ-ray. In both cases, the pH values are determined at 2.0 ± 0.5. Then, it is possible to predict the acidic conditions during the 211 At production by HCl radiolytic yield determination. This work demonstrated that the radiolysis induced by At during its production in CHCl3 medium should be taken into account as it has a significant effect on acid-basic conditions. The work helps understanding the mechanisms of production of a major impurity generated from 211 At radiolysis in chloroform which alters its radiochemistry, allowing for the identification of solutions to counteract these unwanted effects.