The study assessed the level of environmental disclosure practice of manufacturing companies in Nigeria. Anchored on the legitimacy theory, the ex-post facto research design was adopted by the study. The sample was drawn from the population of sixty quoted manufacturing companies on the floor of the Nigerian Stock Exchange as at 31 December, 2017 using the judgmental sampling technique. The study variables were sourced from the annual reports and the stand-alone environmental reports of the selected companies from 2007-2017. The Global Reporting Initiative (GRI) environmental disclosure index was adopted in assessing the disclosure practice of the companies over the years. The findings showed that the environmental disclosure practice of the quoted manufacturing companies was low in the areas of material, energy, emissions, effluent and waste, water and biodiversity. A good number of the manufacturing companies disclosed very well the theme “others” in the area of environmental expenditure and investment. The study further observed a non-significant statistical difference in the disclosure practice of manufacturing companies over the years (t = -1.440, p = .223). The study concluded that there exists no significant difference in the level of environmental disclosure practice of manufacturing companies in Nigeria from 2007 to 2017.