Gelation is one of the major defects in UHT milk products as it limits the shelf life of the products. The role of Bacillus cereus and bacterial proteinases in gelation of UHT milk during storage was investigated. Samples of UHT milk were inoculated with B. cereus and stored at 4, 25, and 37°C for 7 d. Gelation and pH of milk were monitored during storage. Proteolysis was assessed by electrophoresis, soluble nitrogen and liquid chromatography. Gelation was detected in samples inoculated by B. cereus stored at 37°C for 12 h when count reached 8.87 to 10.3 log cfu/mL. At 25°C, the gelation was observed after 48 h at a count of 8.6 to 9.3 log cfu/mL. The pH values of inoculated samples during storage at 25 and 37°C decreased from 6.65 to 5.3 and 5.8, respectively. The samples stored at 4°C did not show any increase in count and pH changes thus, there was no gelation. The gel electrophoresis of casein breakdown showed that proteinases enzymes secreted by B. cereus degraded κ-casein extensively after 6 h, where after 9 h storage, β-casein and much of the α-casein was degraded after 12 h (time of gelation). The levels of soluble nitrogen were high due to the enzymatic activity that caused gelation after storage. The peptide profiles showed that the peaks eluted after 1, 3, 6, 9, 12, and 24 h of storage. The peaks represented the largest, least acid-soluble as well as the most hydrophobic peptides and represent the peptides produced from κ-casein hydrolysis. The profiles were different in 12 and 24 h of storage. Further, new peptides were eluted due to continuing extensive proteolysis that led to the release of more hydrophilic and hydrophobic peptides. The results indicate that gelation of UHT milk correlated well with the growth of B. cereus and changes in pH during storage. Bacterial proteinase enzymes hydrolyzed casein and cause gelation during storage of UHT milk.