Objectives: Mucopolysaccharidosis type I (MPS I) is a rare genetic diseases caused by a deficiency of α-L-iduronidase (IDUA) resulting from a variation in IDUA gene. Although severe or fast progressing MPS I is usually diagnosed in young children, the attenuated or slow-progressing form develops slowly and insidiously and is often not diagnosed until the patient is an adolescent or an adult. Since it has been reported that kidney is one of organs representative of the accumulation of a large amount of glycosaminoglycans, we examined the prevalence of the attenuated form of MPS I in adult patients with chronic kidney disease (CKD). Methods: From May 2018 to December 2021, 1,957 CKD patients were screened using the direct assay of IDUA in dried blood spot. Of these patients, 147 patients with a reduction of IDUA activity (less than 1.15 times the lower limit of normal) were recommended to have the genetic analysis for IDUA gene. Results: In the results of molecular gene analysis of 40 patients, 2 patients had no variation in the IDUA gene while 30 variation alleles in the IDUA gene were found in 38 patients. Of the variation alleles, one of 30 IDUA mutations was identified as being pathogenic (c.1598C>T [p.P533L]), and the most common benign IDUA variation allele was c.99T>G [p.H33Q]. Although most other variation IDUA variation alleles or polymorphisms have been reported to be benign or likely benign, clinical significances of five mutation alleles including c.494-57G>T, c.984G>C [p.Q328H], c.1328G>A [p.S443N], c.1524+53G>T and c.1728-39G>A were not reported in database. Conclusions: A considerable number of IDUA variation alleles were found in CKD patients and most patients were presumed to be affected with the attenuated disease variants. Further research is needed to investigate whether these mutants could affect long-term renal outcome in patients with CKD.