A 3-D printed metallic circularly polarized (CP) antenna with dual-cavity structure and enhanced axial ratio (AR) bandwidth is proposed in this paper. On the one hand, grooved circular open-ended waveguide is here utilized to generate CP waves. On the other hand, another waveguide with approximate dimension is adjacent and connected to the primal one, thus working as a parasitic radiation element and enhancing the AR bandwidth. By virtue of selective laser melting (SLM), a kind of 3-D printing technologies, the proposed antenna can be easily fabricated with high precision and low cost, and then goes through test. The measured 3-dB AR bandwidth is 1.25 GHz (9.05-10.3 GHz), which has been enhanced from 5.8% of single-cavity case to 12.9%.