The Lightest Kaluza-Klein particle (LKP), which appears in the Universal Extra Dimension theory (UED), emits gamma-ray directly or secondarily, when it annihilates. The gamma-ray signal from annihilation of LKP will create prominent structure around the LKP mass, and we expect the structure can be observed by using ongoing and near-future space-based detectors with a few percent energy resolution. On the other hand, ground-based detectors, such as HESS, have 15-20% energy resolution, so we could not see a peak structure in the gamma-ray spectrum from LKP annihilation. However, by using HESS observational data, even if the peak structure does not seem to appear in the gamma-ray spectrum, we can set constraints on the boost factor, which determines the density distribution and the annihilation cross section of dark matter in the Galaxy. In addition, we discuss how we can set constraints on the boost factor, when the high accuracy gamma-ray observational data is obtained by space-based detector.