This study compared psychometric properties of the Taiwanese version of the Quality of Life after Brain Injury (QOLIBRI) between patients with mild and those with moderate/severe traumatic brain injury (TBI). Of 683 participants, 548 had sustained a mild injury with Glasgow Coma Scale (GCS) scores of 13–15, and 135 had a moderate/severe injury with GCS scores of 3–12. The QOLIBRI comprises six domains: Cognition, Self, Daily Life and Autonomy, Social Relationships, Emotions, and Physical Problems. Results of the Rasch analysis showed that two items of “Problems with seeing/hearing” and “Finding one’s way about” were underfitting in the mild TBI group while the item “Problems with seeing/hearing” was underfitting and the item “TBI effects” was overfitting in the moderate/severe TBI group. The largest differential item functioning (DIF) between the mild and moderate/severe TBI groups appeared in the item “Energy,” followed by those of “Being slow/clumsy” and “Problems with seeing/hearing.” For both the mild and moderate/severe TBI groups, the two domains of Emotions and Physical Problems displayed strong ceiling effects, low person reliability and separation, and an incomplete range of the person measure covered by the item difficulty, while the remaining four domains had acceptable performances. While the psychometric performance of the QOLIBRI at the domain level was similar between the mild and moderate/severe TBI groups, certain items exhibited different functioning between the two groups. The reason why the two domains of the Emotions and Physical Problems performed poorly in the two TBI severity groups could be due to cross-cultural effects. The meanings of these DIF items, particularly for patients with a mild TBI, and factors contributing to the ceiling effect of the Emotions and Physical Problems domains in other ethnic Chinese populations need to be investigated further.