This study examined the link between audit quality and agency costs in Nigeria corporate environment. Specifically, the study examined the way audit quality represented by audit firm size affect agency conflicts represented by asset utilization rate, and whether timeliness of the audit report alters the nexus between audit quality and agency conflicts in Nigeria. The data were collected from seventy-three (73) listed non-financial firms who consistently published their annual reports between 2010 and 2019 out of the one hundred and twelve (112) non-financial firms listed on the Nigerian Stock Exchange as of 31st December 2020. Descriptive statistics tools of mean and standard deviation as well as correlation analysis were used for preliminary analysis while fixed effect panel regression was used for the multivariate analysis. Feasible generalize least square was used to estimate the model for robustness check in addition to the use Tobin’s Q as alternative proxy for agency conflicts. The results were obtained by controlling for firm size, firm performance, and firm age. The results of the study revealed a significant negative impact of audit quality on agency costs implying that firms audit by big four have significantly lower agency costs compared to firms audited by other audit firms. Further analysis of the results shows that the positive effect of audit report lag overwhelms the negative influence of audit firm size on agency costs suggesting that using big 4-audit firm would not mitigate agency conflict if the audit report lag is higher. These findings are robust to alternate estimation technique and proxy for agency costs. This study therefore recommends that firms should not only patronize big 4-audit firm to mitigate agency conflict, they must ensure timely audit report.