Background The upper limit for liver resections in rats is approximately 90%. In the early postoperative phase, mortality increases. The aim of the present study was to validate the rat model of 90% partial hepatectomy (PH) as a model of post‐hepatectomy liver failure (PHLF). Further, we wanted to test a quantitative scoring system as a detector of lethal outcomes caused by PHLF in rats. Methods Sixty‐eight rats were randomized to 90% PH, sham operation, or no surgery. Further, block randomization was performed based on time of euthanization: 12, 24, or 48 h after surgery. A general distress score (GDS) ≥10 during the day or ≥6 at midnight prompted early euthanization and classification as nonsurvivor. Animals euthanized as planned were classified as survivors. During euthanization, blood and liver tissue were collected, and liver‐specific biochemistry was evaluated. Results Based on the biochemical results, all animals subjected to 90% PH experienced PHLF. Seventeen rats were euthanized due to irreversible PHLF. The GDS increased for nonsurvivors within 12–18 h after surgery. The mean time for euthanization was 27 h after surgery. Conclusion Based on the GDS and liver‐specific biochemistry, we concluded that the model of 90% PH seems to be a proper model for investigating PHLF in rats. As a high GDS is associated with increased mortality, the GDS appears to be valuable in detecting lethal outcomes caused by PHLF in rats. In the present study, we evaluated the rat model of 90% partial hepatectomy (PH) as a model of post‐hepatectomy liver failure (PHLF). We also investigated the use of a quantitative scoring system to detect lethal outcomes caused by PHLF in rats. Based on our clinical scoring system and supported by liver‐specific biochemistry, the model of 90% PH seems to be relevant for investigating PHLF in rats. By including both physiological and behavioral parameters, GDS appears to be valuable in detecting lethal outcomes caused by PHLF in rats.