Background: The prevalence of chronic kidney disease (CKD) increases with age as with idiopathic pulmonary fibrosis (IPF). Objectives: We assessed the prevalence of CKD (stages 3-5) and investigated the relationship of CKD to clinical features and outcomes in patients with IPF. Methods: This study comprised 123 patients with IPF; 61 subjects with chronic obstructive pulmonary disease (COPD), which was reportedly associated with CKD, were also enrolled as a disease control. CKD (stages 3-5) was defined as an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m². Results: Thirty-seven patients (30%) with IPF and 14 controls (23%) with COPD were diagnosed with CKD, and these frequencies were not significantly different. The patients with IPF and CKD were older (p < 0.01) and had a higher frequency of hypertension (p = 0.048) and ischemic heart disease (p = 0.02) than those with IPF but without CKD. Furthermore, the diffusing capacity of the lung for carbon monoxide (DLCO) and the 6-min walking distance in the patients with CKD were significantly lower (40.0 ± 13.2 vs. 45.9 ± 14.4%, p = 0.04, and 416 ± 129 vs. 474 ± 84 m, p = 0.01, respectively) than in the patients without CKD. The outcome of the patients with CKD showed significantly worse survival compared with the patients without CKD (p = 0.04). Moreover, eGFR remained an independent predictor of survival after adjusting for age and pulmonary function data. Conclusion: A substantial percentage of IPF patients have CKD. CKD with a low eGFR was associated with decreased survival in IPF.