The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has evaluated the maximum concentration at the workplace (MAK value) of N‐(1,3‐dimethylbutyl)‐N′‐phenyl‐p‐phenylenediamine, considering all toxicity endpoints. Available unpublished study reports and publications are described in detail. Critical effects of N‐(1,3‐dimethylbutyl)‐N′‐phenyl‐p‐phenylenediamine are increased liver weights, changes in haematological parameters with mild anaemia after higher doses and its skin‐sensitizing property. The chronic NOAEL in male rats is 2.6 mg/kg body weight based on effects on the liver which can be used to calculate a MAK value of 2 mg/m3 for the inhalable fraction. This value also provides protection from irritation. As the critical effect is systemic, Peak Limitation Category II is assigned. The default excursion factor of 2 is set as no half‐life in blood is known. Damage to the embryo is unlikely if the MAK value for N‐(1,3‐dimethylbutyl)‐N′‐phenyl‐p‐phenylenediamine is observed and the substance is classified in Pregnancy Risk Group C. N‐(1,3‐dimethylbutyl)‐N′‐phenyl‐p‐phenylenediamine is a skin sensitizer and the designation with “Sh” is assigned. There are no data concerning the potential for respiratory sensitization. Skin contact is not expected to contribute significantly to systemic toxicity. N‐(1,3‐dimethylbutyl)‐N′‐phenyl‐p‐phenylenediamine is not genotoxic or carcinogenic.