We investigate the effects of a polyelectrolyte chain's configurational fluctuations on the counterion condensation theoretically. Starting with a straight‐line configuration where the polyelectrolyte chain is totally stretched, the configurational fluctuations are developed by relaxing the stretch. The amount of relaxation appears as a control parameter for configurational fluctuations in this model. The electrostatic potential generated by the fluctuating polyion is obtained through a perturbation calculation around the straight‐line configuration. Adopting the obtained electrostatic potential and using a two‐phase model calculation, the fraction of condensed counterions in the system is calculated. Effects of the Manning parameter and the fluctuations are discussed. In particular, it is shown that configurational fluctuations lead more counterions to be condensed. These observations can be understood in a transparent way in the model.
