A plastic glass optical fiber includes a glass core (diameter a1, relative refractive index difference Δ1, and refractive index n1), a polymer core (diameter a2, relative refractive index difference Δ2, and refractive index n2), and a polymer cladding (refractive index n3), in which the diameter a1 of the glass core is within a range of 110 μm to 200 μm, a parameter X (X is a22/a12) is within a range of 1.15≦X≦2.9, a parameter Y (Y is Δ2/Δ1) is within a range of 0.25≦Y≦0.84X−0.68 (when 1.15≦X≦2) or 0.48X−0.71≦Y≦−(2/9)X+13/9 (when 2≦X≦2.9), a parameter ZR (ZR is Z2core/Z1core; Z2core=a22π/4×√(n12−n32) and Z1core=a12π/4×√(n12−n22)) is within a range of 1.25≦ZR≦4.