Background/objective <p>Data regarding to how muscle mass and function affect mortality in newly initiated peritoneal dialysis (PD) patients have led to inconclusive results. The goal of this research was to determine the relationship between sarcopenia and the risk of mortality among end-stage kidney disease (ESKD) patients who were newly initiated on PD.</p> Methods <p>Patients were prospectively recruited among newly initiated PD patients with ESKD, and followed up at regular intervals from January 2021 to June 2024. The status of sarcopenia in the baseline visit was the exposure of interest. The death event during the follow-up period was the primary outcome. Kaplan-Meier analysis with log-rank test was used to compare overall survival between groups. Confounders were adjusted by employing Cox proportional hazards models.</p> Results <p>298 eligible participants were included for the final statistical analysis. Among these 298 participants, the prevalence of sarcopenia was 40.9% (122), of which the prevalence of non-severe sarcopenia was 22.1% (66) and that of severe sarcopenia was 18.8% (56). During the 6730 person-months of follow-up (median 25 months, maximum 42 months), 22.1% (66) participants died. Of these, 30.3% (37) were in the group with sarcopenia and 16.5% (29) were in the group with non-sarcopenia, with an absolute difference of 13.8% (95%CI 4.0%-23.6%). The Kaplan-Meier survival curve revealed that the participants with sarcopenia had a poorer survival rate compared to those without sarcopenia (Log-rank test, χ² = 14.7, <i>P</i> &lt; 0.001). After adjustment for potential confounding factors, patients diagnosed with sarcopenia were significantly correlated with an increased risk of all-cause mortality (HR = 2.90, 95%CI 1.72–4.90, <i>P</i> &lt; 0.001). The relationship between sarcopenia (severe sarcopenia vs. non-sarcopenia; non-severe sarcopenia vs. non-sarcopenia) and mortality was consistent (HR = 2.57, 95%CI 1.42–4.66, <i>P</i> = 0.002; HR = 3.56, 95%CI 1.83–6.91, <i>P</i> &lt; 0.001) in sensitivity analysis. In subgroup analysis, the relationship between sarcopenia and all-cause mortality remained consistent (HR = 8.63, 95%CI 3.17–23.51, <i>P</i> &lt; 0.001) in participants with age ≥ 60 years; however, no significant relationship was identified in patients with age &lt; 60 years (HR = 1.56, 95%CI 0.75–3.25, <i>P</i> = 0.24).</p> Conclusion <p>Our study demonstrated that the status of sarcopenia was significantly associated with an increased risk of mortality in ESKD patients who newly initiated PD, especially in elderly individuals.</p>