We investigated the upconversion (UC) properties of YBO3 co-doped with Er3+ and Yb3+ ions. The YBO3 samples were synthesized by the solid state reaction method. The Er3+ and Yb3+ were doped at various ratios into YBO3 to investigate the effect of concentration of the Er3+/Yb3+ ions on the UC emission. Rietveld refinement was performed on the X-ray diffraction patterns to obtain the crystal structural parameters. Strong red and green UC emissions were observed from Er3+ and Yb3+-codoped YBO3 under 980 nm diode laser excitation. The highest UC emission efficiency was achieved at 5 mol% concentration of both the Er3+ and Yb3+ ions. The power-dependent UC emission spectra of our samples indicate that the red UC emission of Er3+ should originate from a two-photon absorption process.