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Due to its low sensitivity to blackbody radiation, neutral mercury is a good candidate for the most accurate optical lattice clock. Here we report the observation of cold mercury atoms in a magneto-optical trap (MOT). Because of the high vapor pressure at room temperature, the mercury source and the cold pump were cooled down to −40 °C and −70 °C, respectively, to keep the science chamber in an ultra-high vacuum of 6 × 10−9 Pa. Limited by the power of the UV cooling laser, the one beam folded MOT configuration was adopted, and 1.5×105 Hg-202 atoms were observed by fluorescence detection.