Objectives: Hypoalbuminemia at the start of continuous renal replacement therapy (CRRT) is a risk factor for poor patient outcomes. However, little is known regarding changes in serum albumin levels during CRRT, or whether the pattern of change can provide additional information to predict patient outcomes.   Methods: This was a retrospective study based on the consecutively collected data from January 2016 to December 2020 at the Third Affiliated Hospital. We included acute kidney injury patients who received CRRT more than 72 hours. We divided the patients into four groups based on their serum albumin level at the initiation and termination (albumin ≥ 3.0 g/dL or < 3.0 g/dL) of CRRT. Results: Of the 793 patients included, 299 (37.7%) were categorized into the persistently low, 85 (10.4%) into the increasing, 195 (24.6%) into the decreasing, and 214 (27.10%) into the persistently high albumin groups. The in-hospital mortality rates were highest in the persistently low and decreasing groups, followed by the increasing and persistently high groups. The hazard ratio (HR) for in-hospital mortality was 0.481 (0.340, 0.680) in the increasing group compared to the persistently low group, while the HR for in-hospital mortality was 1.911 (1.394, 2.620) in the decreasing group compared to the persistently high group. The length of ICU stay was longer in the persistently low group by 3.55 days compared to the persistently high group. Conclusions: Serum albumin levels changed during CRRT, and monitoring of serum albumin provided additional information for predicting in-hospital mortality and duration of ICU stay.