ZnO based oxide system Be (x) Zn1-x O alloy of various compositions has been successfully grown by the RF co-sputtering method. The crystallinity of the Be (x) Zn1-x O alloys has been remarkably improved after the post-annealing at 600 A degrees C compared with the Be (x) Zn1-x O alloys post-annealed at other temperatures. The x value of the Be (x) Zn1-x O layers has been increased from 0.022 to 0.17 by adjusting the RF-power of the Be target. Also, the optical bandgap energy has been modulated from 3.2218 to 3.7978 eV, respectively. Based on our results, a bandgap bowing parameter of Be (x) Zn1-x O alloy has been extracted out to be 4.5 eV. These findings could be useful to fabricate the ZnO/Be (x) Zn1-x O quantum structures and bandgap modulation for deep ultraviolet-light-emitting diodes.