Introduction. In addition to efficacy, purity and safety, stability is an important component for ensuring the quality of a drug. Objective of the study. Evaluation of the stability of dioxoindolinone under stress. Material and Methods. Stability testing methodology ICH Topic Q1A (R2); 3 series of dioxoindolinone in bulk; Shimadzu UV-1800 spectrophotometer; solvents, reagents in accordance with the European Pharmacopoeia. Results. In conditions of oxidative, hydrolytic, thermal, acidbase, photocatalytic stress, it was determined by the UV-VIS spectrophotometric method that the substance is stable in humidity and in an acidic environment. Dioxoindolinone degrades under the influence of the oxidant, it is unstable in a basic environment. The influence of light as well as the simultaneous action of high temperature and have been demonstrated. By experimental storage using the "Accelerated Degradation" method at 40 0C and 60 0C with concentration determination using the UV-VIS spectrophotometric method, the shelf life for the substance was calculated to be 5 years. Conclusion. The results obtained will also be confirmed by real-time stability studies. Currently, the substance is stored under normal conditions (250C; 65% RH) for 4 years and 10 months. So far, the medicinal substance corresponds to all the quality criteria stipulated in the draft specification.