This study examines the moderating effect of firm size on the associationbetween institutional ownership and integrated reporting of listed non financial services firms in Nigeria. The study covered a period of 10 years, 2012 to 2021, and extracted secondary data from a sample of 58 firmslisted on the Nigerian Exchange Group as of 31 December 2021. Thesampled firms were selected from a population of 105 quoted non financial services firms. The study adopted multiple regression analysis, and the results reveal that integrated reporting is strongly influenced by institutional ownership and firm size before moderation. After moderation, the results reveal that the higher the firm size, the lower the influence of institutional owners on integrated reporting. Thus, this study concludes that the presence of institutional ownership in large organizations may reduce integrated reporting. The study recommends that regulators should institute gradual enforcement of integrated reporting among companies in Nigeria.