**Background:** Nigeria’s Basic Health Care Provision Fund (BHCPF) was established to improve access to primary healthcare and provide financial risk protection, particularly for vulnerable populations such as informal sector workers. A systematic national assessment of its impact was needed.

**Purpose and objectives:** This national survey aimed to evaluate the effect of the BHCPF on financial protection and healthcare service utilisation among informal sector households in Nigeria from 2021 to 2023.

**Methodology:** A cross-sectional household survey was conducted across all six geopolitical zones. A multi-stage stratified sampling design selected 4,800 informal sector households. Data were collected via structured questionnaires on healthcare expenditures, service use, and BHCPF awareness. Financial protection was measured by the incidence of catastrophic health expenditure.

**Findings/Key insights:** Awareness of the BHCPF among eligible informal sector households was low (approximately 32%). In areas with active BHCPF-accredited facilities, a lower incidence of catastrophic health spending was observed compared to non-accredited areas. Utilisation of specified maternal and child health services showed modest improvement where the fund was operational.

**Conclusion:** The BHCPF demonstrates potential to enhance financial protection and service use, but its reach and awareness among the informal sector remain limited. Systemic implementation challenges constrain its intended nationwide impact.

**Recommendations:** Scale up strategic communication to increase BHCPF awareness and streamline enrolment for informal workers. Strengthen monitoring to ensure accredited facilities are functional and essential medicines are available.

**Key words:** health financing, financial protection, informal sector, primary healthcare, catastrophic expenditure, Nigeria.

**Contribution statement:** This study provides the first nationally representative evidence on the BHCPF's early effects on informal sector households, offering critical data for policymakers to refine this major health financing reform.