A simple, economical, and specific analytical method has been developed for determining and validating linagliptin (LNG) in bulk. This method is based on a condensation reaction between a primary amine in LNG and an aldehyde group in P-dimethylaminobenzaldehyde (PDAB) to form the yellow Schiff base with a wavelength of 407 nm. The optimum experimental conditions for the formulation of the colored complex have been studied. The optimum conditions were 1 mL of 5% w/v reagent solution with methanol and distilled water as a solvent for both PDAB, LNG respectively, also adding 2 mL of HCl as an acidic medium, heating to 70–75 °C on a water bath for 35 min. Furthermore, the stoichiometry of the reaction has been studied according to Job’s and Molar ratio method which was expressing 1:1 for LNG and PDAB. The researcher modified the method. The results show that the linearity in the concentration range (5–45 µg/mL) with correlation coefficient R 2 = 0.9989 with percent recovery (99.46–100.8%) and RSD was less than 2%, LOD and LOQ 1.5815 − 4.7924 μg/mL respectively. This method can show high quality and there is no significant interference with excipients and in pharmaceutical forms. None of the studies showed the development of this method before.