Background <p>Recent studies have shown a relation between red blood cell distribution width (RDW) / albumin (RAR) levels and worse outcomes in cases of pulmonary embolism (PE). Simplified pulmonary embolism severity index (sPESI) has been developed from more complex PESI score, predicting the risk of death in patients with acute PE (APE). This study aims to investigate whether RDW-Standard Deviation/Albumin (RDW-SD/Alb) can serve as a useful prognostic marker for APE and enhance the predictive capability of the sPESI.</p> Methods <p>This research is a single-center, retrospective analysis involving patients over 18 years. We enrolled 235 consecutive hospitalized patients with confirmed APE diagnoses. To evaluate the sensitivity and specificity of RDW-SD/Alb, sPESI, and the combined sPESI plus RDW-SD/Alb in predicting 6-month all-cause death, we used Receiver Operating Characteristic (ROC) curves. Additionally, we conducted Kaplan–Meier analysis to assess the impact of elevated RDW-SD/Alb levels (&gt; 13.6) on patient survival time. We utilized multivariate Cox regression analysis to identify independent prognostic factors affecting patients survival.</p> Results <p>The mortality rate for RDW-SD/Alb &gt; 13.6 group was significantly higher than that for the RDW-SD/Alb ≤ 13.6 group. Area under ROC (AUROC) of sPESI plus RDW-SD/Alb was statistically larger than AUROC of sPESI (<i>p</i> = 0.025). In the fully adjusted model, increased RDW-SD/Alb levels were consistently linked to all-cause mortality within six months of admission.</p> Conclusions <p>The predictive value of the sPESI for 6-month all-cause death improved when the RDW-SD/Alb &gt; 13.6 parameter was included. RDW-SD/Alb, a novel inflammatory marker, was an independent prognostic factor for predicting 6-month all-cause mortality in patients with APE.</p>