We report the detection of HCN on Jupiter. Three R-branch lines of the ν2 fundamental of HCN near 13.5 μm were observed in absorption, from which the HCN column density is inferred to be 5 × 10-3 cm-am with an uncertainty of a factor of 2. If emission from the stratosphere exists, then the derived column density is only a lowe limit. We suggest that the Jovian HCN most likely originates from the photolysis of CH4 and NH3 in the lower stratosphere and upper troposphere. In addition, an upper limit of 2.5 × 10-2 cm-am was established for the column density of HCN on Saturn.