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Audit firms play a critical role in Nigeria’s corporate sector by independently examining and verifying financial records to ensure accuracy, regulatory compliance, and stakeholder assurance.

In 2025, seven audit firms generated a combined revenue of N37.08 billion, up from N28.76 billion in 2024.

These revenues were earned from auditing major listed companies such as Zenith Bank, UBA, Access Holdings, Transcorp, Seplat, and Dangote Cement, as well as non-listed firms with annual turnover exceeding N100 billion, otherwise known as NMX 100.

The growth reflects the increasing complexity of corporate financial reporting and the demand for professional assurance services among high-turnover organizations.

While the metrics focus on companies with turnover above N100 billion, the audit firms also serve other clients not listed on the Nigerian Exchange Limited (NGX) or with smaller turnovers.

Below is a list of the seven largest audit firms in Nigeria for 2025, based on their earnings from the largest NGX-listed companies.

SIAO Partners generated N31.5 million in revenue in 2025, derived solely from auditing MRS, the only company under its portfolio for the year.

Founded in 2005 through the merger of four audit firms, SIAO Partners is a prominent Nigerian professional services firm providing audit, tax, accounting, and advisory services to both local and international clients. The firm is headquartered in Ikoyi, Lagos, and has built a reputation for delivering high-quality professional services.

The name ‘SIAO’ represents the founding partners—Smith, Ighodalo, Adewale, and Odiachi. The firm employs over 150 professionals, offering both local insight and international expertise to its clientele.

Despite the small revenue figure relative to other top firms, SIAO Partners continues to maintain a focused and specialised client base.