The aim of this study is to compare the efficacy depending on the order of the sequential combination method using sodium picosulfate and magnesium citrate (PMC) and PEG with ascorbic acid for bowel preparation.

The investigators designed this study as a phase II prospective randomized parallel arm clinical trial. 71 participant will be enrolled in each group (142 in total).

The primary outcome is the efficacy of bowel preparation. secondary outcomes are tolerability, side effect of the drugs, polyp detection rate and adenoma detection rate.

Inclusion Criteria:

• Age: 20-75 Patients who visited the outpatient clinic for colonoscopy Patients who agreed to participate in this study

Exclusion Criteria:

• pregnancy, breast feeding stage 3-5 chronic kidney disease (glomerular filtration rate < 60 mL/min/1.73m2), inability to maintain adequate fluid intake, pre-existing electrolyte disturbances, symptomatic congestive heart failure, recent (within < 6 months) symptomatic ischemic heart disease (unstable angina or myocardial infarction).

toxic megacolon active colitis Allergic to drug altered mental status Nausea and vomiting Hyperphosphatemia glucose-6-phosphate dehydrogenase deficiency Hereditary Phenylketonuria Patients with a history of colon surgery Abdominal operation within 6 months