The technique of simultaneous quantitative determination of mineral N soil forms (nitrates, exchangeable and non‐exchangeable ammonium, and total amount of these compounds) and sample pretreatment for the analysis of15N:14N ratio is suggested. The technique is based on the selective association of NH4+‐ions into indophenol complex and subsequent ethyl‐acetate extraction of this complex from solution. The mineralization of indophenol is carried out in alkaline medium with simultaneous NH3distillation into H2SO4titrant. The application of given technique allows us to shorten significantly the time required for analysis and to increase the accuracy of analytical determination.