There have been discoursed regarding the issue of quantity of annual report disclosure as to what the optimal level of accounting policy information that is useful without blinding the user with distracting and irrelevant information. Diverse influencers have been found to have a significant effect on the quantity of the annual report in which company size is not left out, even though they presented inconsistency in their findings. Therefore, this study examines the effect of firm size on quantity of annual reports disclosure in Nigerian quoted companies. Firm size is proxy using the firm total asset which is the independent variable while the dependent variable which is the quantity of annual report is measured by the volume of firm’s annual report. The expo facto research design was used for the study. The population of this study covers all 189 quoted companies on the Floor of the Nigerian Stock Exchange. A sample of 70 selected companies from the year 2009-2019 was used for the study. Preliminary analysis such as descriptive analysis was first conducted and then the panel data regression was conducted. The findings reveal a positive and significant relationship between firm size on quantity of the annual report disclosure proxy by total volume of annual reports. That is, an increase or change in the firm size (total asset), will have a significant increase or changes in the quantity of annual report. The study concludes that firm size plays an important role in the trend of annual reports quantity. The study recommendation is that annual report of firm should only contain relevant financial and non-financial information such as in their earnings, income, turnover, and workforce that will guide users of the annual report in making decisions and motivate investors instead of filling the report with irrelevancies due to the organization expansion and growth.