Platelet-derived growth factor receptors (PDGFRs) are now considered promising targets for the treatment of osteosarcoma. Herein, the design, synthesis, and structure-activity relationships (SAR) of novel pyrimidine-2,4-diamine derivatives that selectively inhibit PDGFRα/β kinases have been studied. The screening cascades revealed that <b>7m</b> was the preferred compound among these derivatives, with IC<sub>50</sub> values of 2.4 and 0.9 nM for PDGFRα and PDGFRβ, respectively. Moreover, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) experiment revealed that <b>7m</b> has a substantial cytotoxic effect against all osteosarcoma cancer cell lines; <b>7m</b> also displayed robust antitumor effects and low toxicity in a xenograft model. Additionally, <b>7m</b> showed excellent bioavailability (<i>F</i> = 62.9%), suitable half-life (<i>T</i><sub>1/2</sub> = 2.12 h), satisfactory metabolic stability, and weak CYP isoform inhibitory activity, suggesting that <b>7m</b> is a potential drug candidate for PDGFR-driven osteosarcoma.