Fourier transform infrared (FTIR) spectroscopy is a powerful method to determine the doping induced structural changes and electronic band structure modifications of conjugated polymer films. Here, we report in situ attenuated total reflection (ATR) FTIR spectroelectrochemical results of reduction reactions (n-doping) of the conjugated ladder polymer polybenzimidazophenanthroline, BBL. The ATR-FTIR spectra are recorded in situ during continuous potential cycling of a BBL coated germanium reflection element in a three electrode spectroelectrochemical cell. The spectra and the structural changes during the reduction (n-doping) of the polymer film at different electrode potentials are presented. In contrast to most of the other conjugated polymers, this polymer shows four reversible redox reactions during n-doping, corresponding to various forms of BBL with different conductivities.