Background: Limited information is currently available on the barriers to implementing mobilization at the bedside for critically ill patients. Therefore, we investigated the current practice of and barriers to the implementation of mobilization in intensive care units (ICU).Methods: A multicenter prospective observational study was conducted at nine hospitals between June 2019 and December 2019. Consecutive patients admitted to the ICU for more than 48 h were enrolled. Quantitative data were analyzed descriptively, and qualitative data were analyzed thematically.Results: The 203 patients enrolled in the present study were divided into 69 elective surgical patients and 134 unplanned admission patients. The mean periods of time until the initiation of rehabilitation programs after ICU admission were 2.9 ± 7.7 and 1.7 ± 2.0 days, respectively. Median ICU mobility scales were five (Interquartile range: three and eight) and six (Interquartile range: three and nine), respectively. The most common barriers to mobilization in the ICU were circulatory instability (29.9%) and a physician’s order for postoperative bed rest (23.4%) in the unplanned admission and elective surgery groups, respectively.Conclusions: Rehabilitation programs were initiated later for unplanned admission patients and were less intense than those for elective surgical patients, irrespective of the time after ICU admission.