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Abstract. Polypropylene bags (100 kg capacity) are used by farmers in many African countries for handling, marketing and storage of grain. Though high postharvest losses have been reported in polypropylene bag storage systems, only few researches have reported the impact of warehouse environments on the microclimate and the quality of stored grain. This study investigated the effects of warehouse temperature and relative humidity at two locations (Ilorin, Nigeria and Lexington, KY, USA) on corn (initially at 10% and 14% moisture content wet basis, respectively) in polypropylene bags. A monitoring system having multiple data loggers placed under the roof and pallets, spaces between bags and inside selected bags provided the temperature and relative humidity profile within the warehouse and the micro-climate of selected bags from May 3 to Sep 9, 2019 at Ilorin and Dec 8 to Apr 8, 2020 at Lexington (four months). Temperature and relative humidity in the warehouse at Ilorin ranged between 23—31°C and, 60—82%, respectively, and from -1—20°C and, 39—95%, respectively, at Lexington. EMC of bagged corn was determined by the modified-Henderson equation and increased by 1.2% and 0.5% (wb), at Ilorin and Lexington, respectively. Insect damaged kernels in the Ilorin warehouse and percent weight loss ranged between 7 – 24% and 0.1 – 18% respectively after four months of storage. There was a significant difference in the number of insects present in bags at different layers of the stacks. The result indicated that grain stored in polypropylene bags was not protected from moisture ingress from the ambient air in the warehouses, as expected. Combined with warm temperatures, the micro-climate of bagged grain was conducive for insect growth at Ilorin, as expected.