The problem of poor accuracy and credibility in some audited financial statement has being a major form of information asymmetry which had led some shareholders and prospective investors to make wrong Judgment about the financial position of some organization due to poor audit quality. Thus, Specifically this study empirically examine how audit fee, audit report lag as well as mandatory auditor rotation affect the audit quality of the sample listed pharmaceutical firms on the floor of the Nigerian Stock Exchange. A GLS estimation method was employed to clearly establish the nature relationship that exists between the dependent variable and the adopted surrogates for the independent variables. A Secondary data was extracted from the annual audited reports from the ten selected pharmaceutical firms that serve as the fair representation for the population under study for a period of ten years 2009-2019. The result from the finding shows that all the adopted surrogates for the independent variable were jointly significant in explaining about 72% variation in audit quality given credence to the coefficient of (R2) which stood @ 0.72 as well as the combined p-value of 0.000. This implies that the predictive power of the surrogates of the independent variables can explain about 72% changes in audit quality of the population under study. In specific terms; Audit fee have a significant positive impact on audit quality of the selected pharmaceutical firms while audit report lag and mandatory auditor rotation have significant negative impact the audit quality of the selected pharmaceutical firms respectively. The study therefore recommends among many others that policy makers and regulators should put in place a framework that will ensure the payment of optimal compensation to audit firm as audit fee as this will no doubt go a long way in improving the audit quality of the firms under study.