The uterus starts shrinking after giving birth and returns to its size prior to pregnancy one month postpartum. However, absence of this natural shrinking is called uterine subinvolution. There are two types of subinvolution : organic and functional. Removal of the cause is the first option for organic subinvolution. Conversely, most cases of functional subinvolution require drug treatment. This study included patients with subinvolution caused by accumulation of lochia with a uterine cavity width of 15 mm or more during a 14-day postpartum checkup. These patients were categorized into the control, keishibukuryogan, and ergometrine maleate groups ; therapeutic intervention was performed. A comparative study was conducted to determine the presence of subinvolution during the 1-month medical screening. There was no difference in the rate of uterine cavity shrinkage between the ergometrine maleate group and the control group. However, the keishibukuryogan group had a significantly higher reduction rate than the ergometrine maleate group. Furthermore, the keishibukuryogan group showed a tendency of higher shrinking rate when compared with the control group (76.1 ± 17.1% vs 65.8 ± 25.4%, 68.3 ± 22.9%, p = 0.0101, p = 0.0709). Additionally, no difference in the reduction rate of the fundal height was noted among the groups. These results suggest that although keishibukuryogan has little effect on reducing the uterine size, however, it has the effect of lochia accumulated within the uterine cavity.