The ZnO nanoneedles (ZNNs) were grown in large quantity by thermal evaporation technique on non-catalytic Si (100) substrates and used as an effective photocatalyst for photocatalytic degradation of methyl orange dye (MO). The detailed characteristics of ZNNs confirmed that the synthesized nanostructures are grown in high density and exhibit well-crystallinity with good optical properties. The photocatalytic properties of ZNNs were investigated under UV light irradiation. A fast decomposition of the MO dye was observed with a degradation rate of ~95.4% within 140 min.