In this study, it was aimed to examine the changes in serum levels of 25-hydroxyvitamin D [25-(OH)D], parathyroid hormone (PTH), calcium (Ca), and phosphorus (P) in cattle with dermatophytosis. 28 cattle with dermatophytosis (infected group) and 14 healthy cattle (control group) between the ages of 6-8 months composed the study's material. In comparison to the control group, the infected group had significantly lower serum 25-(OH)D levels (P=0.001) while having higher levels of PTH, Ca, and P according to our results. In addition, serum 25-(OH)D levels had a negative correlation with white blood cell (WBC) and neutrophil (NEU) levels. The infected group was divided into two subgroups according to the distribution of lesions as mild and severe. When compared to the control and mild groups, the severe group had the highest WBC (P=0.007) and NEU (P=0.005) values and the lowest 25-(OH)D levels (P=0.000). As a result, it was concluded that vitamin D levels decreased significantly in cattle with dermatophytosis and this situation led to the worsening of the disease by suppression of immunity. PTH elevation was evaluated as the body's response to infection to compensate for vitamin D deficiency. Based on these findings, it was assumed that vitamin D plays a role in disease pathogenesis and is an essential component of the treatment.