Indoor Environmental Quality (IEQ) significantly influences occupant health, comfort, and productivity, yet student accommodation in many developing countries often suffers from poor environmental conditions. This study aimed to evaluate IEQ in university hostel rooms in Southwestern Nigeria, with a focus on thermal comfort, ventilation, and lighting adequacy, and to examine their relationship with symptoms of Sick Building Syndrome (SBS). A total of 143 hostel rooms were assessed for temperature, air velocity, and illumination using standardised field measurement techniques. The measured values were compared against international benchmarks set by the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE), the World Health Organisation (WHO), and the Chartered Institute of Building Services Engineers (CIBSE). Results revealed that all IEQ parameters fell outside recommended limits, with average room temperature at 32.60 °C, mean air velocity at 0.91 m/s, and illumination at 71.11 lux . These conditions were associated with commonly reported SBS symptoms such as sneezing, fatigue, and visual discomfort. The findings highlight that inconsistent ventilation and persistently low lighting levels may undermine occupant well-being and academic performance. It is recommended that targeted interventions, such as improved natural and mechanical ventilation systems, optimised lighting design, and thermal control measures, should be implemented to enhance living conditions in student hostels.