Objective  To investigate the efficacy of iron isomaltoside in peritoneal dialysis (PD) patients with anemia caused by absolute iron deficiency and the effects of different doses on residual kidney function.  Methods  A retrospective analysis was conducted on patients who had undergone regular PD for more than 3 months, with ferritin ＜100 μg/L and transferrin saturation ＜20%. According to the dose of a single intravenous injection of iron isomaltoside, the patients were divided into group A (500 mg) and group B (1000 mg). The retreatment time, hemoglobin, iron metabolism indicators, and changes in residual kidney function were compared between the two groups.   Results  A total of 34 patients were included, with 17 patients in each group. After intravenous iron therapy, ferritin (t=-6.675, P＜0.001), transferrin saturation (t=-5.244, P＜0.001), and hemoglobin (t=-3.986, P＜0.001) increased. The retreatment time in group A and group B was (3.41±1.33) months and (5.31±2.56) months, respectively, with group A being shorter than group B (t=-2.771, P=0.009); the last ferritin level in group A was lower than that in group B (t=-2.225, P=0.033). In group B, residual kidney Kt/V decreased from 0.35 to 0.23 after iron isomaltoside treatment (Z=-2.556, P=0.011), while there was no statistically significant difference in group A before and after treatment (Z=-1.183, P=0.237).  Conclusion Iron isomaltoside can effectively improve iron metabolism status and increase hemoglobin levels in PD patients with absolute iron deficiency. Intravenous iron at 500 mg and 1000 mg has comparable efficacy in improving anemia, but 1000 mg intravenous iron may be associated with a rapid increase in ferritin and a decline in residual kidney function, and should be used with caution.