Podoplanin (PDPN) is a type-I transmembrane sialoglycoprotein that possesses a platelet aggregation-stimulating (PLAG) domain in the N-terminus. PLAG domain includes three tandem repeats of eight amino acids: PLAG1, PLAG2, and PLAG3. Among the three PLAG domains, O-glycan on Thr52 of PLAG3 is critical for binding with C-type lectin-like receptor-2 (CLEC-2) and is essential for platelet-aggregating activity of PDPN. In contrast, the glycosylation of Thr34 of PLAG1 of human PDPN remains to be clarified. Herein, we developed and characterized a novel anti-PDPN monoclonal antibody, LpMab-10, which targets PLAG1/2 domain. LpMab-10 detects endogenous PDPN of cancer cells and normal cells independently of glycosylation. The minimum epitope of LpMab-10 was identified as Glu33-Gly45 of PDPN using Western blot and flow cytometry. The Thr34 of PLAG1 is critical for LpMab-10 recognition, and O-glycan is not included in LpMab-10 epitope, indicating that Thr34 of PLAG1 is not O-glycosylated. In immunocytochemical and immunohistochemical analyses, LpMab-10 strongly detected PDPN-expressing tumor cells. By using monoclonal antibodies against different Ser/Thr, including epitopes of PDPN, it becomes possible to determine whether Ser/Thr residues of PDPN are O-glycosylated.