Background: Primary Eosinophilic Colitis (PEC) is one of the rare eosinophilic gastrointestinal diseases with a poorly understood pathogenesis. Eosinophilic esophagitis (EE) is the most common and best-understood disease in this category. Activated mast cells (MCs) have a role to play in the tissue damage in EE. It is not known if PEC shares this mechanism. Objective: This cross-sectional study aimed to investigate the number of MCs in PEC and to compare them with cases of secondary colonic tissue eosinophilia (TE) and normal colon. Methods: The study included 19 PEC cases, 47 cases of secondary tissue eosinophilia and 50 normal colon tissues. Histopathological slides of all cases were reviewed to confirm the diagnosis and count the number of eosinophils. Glass slides for all cases were stained for C-kit (CD117) to highlight and count the MCs. Results: The mean number of the MCs in normal controls was 9.7 MCs per HPF (SD= 4.6). The mean number of MCs in the PEC cases was 26.5 (SD=7.1) which was significantly higher than the normal counts (p-value <0.000). The mean number of MCs in the secondary TE group was 18.0 (SD=7.1), which was significantly higher than normal controls; p-value <0.000. Comparing MC counts in PEC and secondary TE also revealed a significant difference with a p-value of < 0.000. Conclusion: MCs in PEC are significantly higher than those in secondary TE and normal controls. This suggests the role of the MCs in the pathogenesis of Primary Eosinophilic Colitis.