This study aimed to determine effects of postpartal relative body weight change (PRBWC) on production performance, serum biomarkers, and the relation between PRBWC and gastrointestinal microbiota. A total of 59 multiparous cows participated in this research. Every cow’s PRBWC was calculated by the following equation: PRBWC = (BW₂₁ − BW₀)/BW₀ × 100%, in which BW₂₁ refers to body weight on Day 21 post-calving and BW₀ refers to body weight on the day of parturition. Among the 59 enrolled cows, cows with the top 21 ranked PRBWC values were categorized into the high PRBWC (H-PRBWC) group; cows with the bottom 21 ranked PRBWC values were categorized into the low PRBWC (L-PRBWC) group. PRBWC did not have significant influences on average daily milk yield (ADMY). However, on Day 21, cows in the H-PRBWC group displayed significantly higher body weight (BW) and body condition scores (BCS) (BW, p = 0.02; BCS, p < 0.01). Additionally, levels of serum glucose (GLU) and albumin (ALB) were significantly higher in the H-PRBWC group on Day 21 (GLU, p = 0.05; ALB, p < 0.01), while the lipopolysaccharide-binding protein (LBP) level was significant lower (p = 0.03). Moreover, the microbiota of fecal samples on Day 0 (FE0) differed notably between groups, as evidenced by various alpha diversity indices, including Shannon (p = 0.02), Simpson (p = 0.03), Pielou_e (p = 0.02), and principal coordinate analysis (p = 0.002). The relative abundances of Monoglobus, norank_f__UCG-010, and Christensenellaceae_R-7_group were significantly higher in the H-PRBWC group (p < 0.05), while the relative abundances of Clostridium_sensu_stricto_1, Turicibacter, and Romboutsia were significantly lower (p < 0.05). Pathways related to amino acid biosynthesis were significantly enriched in the FE0 of the H-PRBWC group, while pathways involved in carbohydrate metabolism were significantly upregulated in the FE0 of the L-PRBWC group. This study argues the potential of PRBWC to describe alteration of energy status in the postpartum, evidenced by production performance, serum biomarkers, and the fecal microbiota.