Amorphous spherical Eu doped YBO3 was synthesized by a mild one-step hydrothermal method. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the as-prepared products. It was demonstrated that the use of urea as alkali source plays the key function in the formation of amorphous spherical YBO3:Eu3+. The crystallinity and the morphologies of the YBO3:Eu3+ were sensitive to the urea content and the hydrothermal time. Room temperature photoluminescence (PL) spectra were detected. The sample in uniform diameter of 300-400 nm had the relative strong red emissions (R) and R/O ratio of 1.3.