The study was conducted in Kilosa District to assess spoilage loss of stored Maize (Zea mays L.) and Groundnuts (Arachis hypogaea L.) due to mycotoxins and its effect on household food security. The sample of approximately 10 kg of maize and 5 kg of groundnuts were stored in a small polythene bag for 9 months. The data collected were maize grains and groundnuts kernel which were later sorted into rotten and discolored and further counted as spoiled grains expressed in percentages. The losses were estimated by the count and weighing method. The damaged kernels were determined and calculated as percentages using the Statistical Analysis System (SAS® Version 9.4). The average weight loss of maize and groundnuts were 20.8% and 14.5% respectively as a result of mycotoxin contamination. The estimated annual revenue loss in U$D was about 179, 116.37 (=268, 674, 555 Tshs) in maize. Further analysis indicated that 22% of farmers lost up to 10 kg of groundnuts and 31.9% of farmers lost up to more than 10 kg of groundnuts as a result of aflatoxin contamination. Maize and groundnuts spoilage in the study area was caused by poor handling and storage conditions such as insufficient drying. Some of the suggested solutions to mycotoxin threat in Kilosa District include: early harvesting, prevention of kernel damage during harvesting, adequate drying and proper storage below 13 % moisture for maize and below 7% moisture for groundnuts, and keeping storage facilities clean and dry.