【Background and objectives】Recently, efforts have been made to preserve the kidneys of patients with chronic kidney disease. Among them, patients with diabetic kidney disease (DKD) are attracting attention due to the high rate of dialysis use. Physical activity in patients with DKD is associated with renal function; thus, frequent physical activity is recommended. This requires an analysis of factors related to physical activity to clarify the targets of physiotherapy interventions. Therefore, the purpose of this pilot study was to elucidate factors of physical function related to physical activity in patients with DKD. 【Methods】Patient demographics, physical activity, knee extension strength, and fatigability were evaluated in a cross-sectional manner. Physical activity was evaluated for total physical activity-International Physical Activity Questionnaire (TPA-IPAQ) (kcal/week) using the IPAQ-short version. Knee extension strength and fatigability were evaluated using a muscle function evaluation exercise device. Fatigability was calculated as the rate of the decrease in torque during a dynamic fatigue task. 【Results】26 patients were enrolled in this study and 23 patients (n = 14 men, mean age 56.4 ± 6.3 years) were included in the analysis. As a result of analysis, physical activity was negatively correlated with fatigability alone (r = -0.416, p = 0.049). 【Discussion】This study suggests that fatigability is associated with decreased physical activity, which may also lead to decreased renal function in patients with DKD. Further research on factors related to physical activity, including an analysis of fatigability, is needed to develop exercise management programs to protect kidney functionality.