The transformation of the Nigerian Prison Service into the Nigerian Correctional Service (NCOs) through the Nigerian Correctional Service Act, 2019 marked a significant shift in Nigeria's correctional philosophy from punishment to rehabilitation and reintegration of offenders. Central to achieving this objective is the effective classification of inmates, which enables correctional authorities to assess offenders according to their security risk, legal status, behavioural characteristics, health condition, age, gender, sentence length, and rehabilitation needs. Appropriate inmate classification promotes institutional security, protects vulnerable inmates, facilitates individualized treatment programmes, and enhances successful reintegration into society. However, despite the legal framework supporting classification, the Nigerian Correctional Service continues to face numerous challenges, including overcrowding, inadequate infrastructure, shortage of trained personnel, limited funding, poor inter-agency collaboration, and reliance on manual record-keeping systems. These challenges undermine effective classification and reduce the efficiency of correctional administration. This study examines the role of the Nigerian Correctional Service in inmate classification, analyses the challenges confronting its implementation, explores opportunities for improvement, and discusses the implications for correctional administration in Nigeria. The study adopts a qualitative research design based on documentary analysis of relevant legislation, policy documents, books, journal articles, and reports from national and international organizations. The findings reveal that effective inmate classification remains indispensable for strengthening institutional security, improving rehabilitation programmes, reducing recidivism, and promoting effective correctional administration. The study recommends increased government funding, modernization of correctional facilities, adoption of evidence-based risk assessment tools, and digitalization of inmate information systems, continuous staff capacity building, and stronger collaboration among criminal justice institutions to enhance inmate classification practices in Nigeria.