The key prognostic factor at the time of diagnosis of upper tract urothelial carcinomas (UTUC) is whether the tumor is in the muscle-invasive or non-muscle invasive stage. It is critical to identify novel molecular biomarkers for early detection and target therapy. Plasma proteins secreted by tumor tissues have excellent potential as biomarkers for UTUC. In this study, we conducted a systematic study to identify plasma markers for UTUC based on RNA-seq data from five UTUC tissues and paired adjacent noncancerous mucosa. Through bioinformatics analysis, we found secreted phosphoprotein 1 (SPP1) was the most significant gene that coding secretory protein. Then, qRT-PCR and enzyme-linked immunosorbent assay were performed to evaluate the expression and clinical significance of SPP1 in UTUC. Results found that SPP1 mRNA was upregulated in UTUC cells and tissues, and high SPP1 mRNA expression level was closely related to advanced stage and high grade. Moreover, it is suggested that plasma SPP1 may be a potential biomarker to help identify early-stage UTUC patients and predict invasive and high-grade UTUC. In conclusion, plasma SPP1 is a novel biomarker for UTUC.