Nanocrystals of undoped and copper doped zinc oxide (Zn1-x Cu x O (where x = 0.00 to 0.05) were synthesized by coprecipitation method. Crystalline phases and optical absorption of prepared samples were determined by X-ray diffraction and UV-visible spectrophotometer. The average particles size was determined from X-ray line broadening. X-ray analyses reveals that Cu doped ZnO crystallizes in hexagonal wurtzite structure. The incorporation of Cu+2 in the place of Zn2+ provoked an increase in the size of nanocrystals as compared to undoped or pure ZnO. Optical absorption measurement indicates red shift in the absorption band edge upon Cu doping. The band gap decreases from 3.15 eV to 2.92 eV with copper (5 %) doping at temperature 450 oC.