Branched ZnO nanorods have been synthesized by hydrothermal process in equimolar of zinc nitrate Zn(NO

3

)

2

·6H

2

O and methenamine C

6

H

12

N

4

aqueous solutions at 90℃ with different growth time.The structures

morphologies and optical properties of ZnO samples have been investigated by X-ray diffraction（XRD）

field emission scanning electron microscopy（SEM） and photoluminescence spectra（PL） at room temperature.We find that the branched prismatic nanorods are evolved by single ZnO nanorod.The results also indicate that the growth time has significant influence on the formation of branched ZnO nanostructures.The PL spectra of the samples show strong yellow-green emission.The Gaussian fitted PL spectra of the ZnO samples reveal that the amount of o

-

i

to v

+

o

defect is much more than that of v

+

o

defect in the unbranched nanorods and the ratio of o

-

i

to v

+

o

defect is relatively lower in the branched nanorods.