Clorprenaline (CLP), a β2-adrenergic agonist, was first found in veterinary drugs for cold treatment in China in 2013. It is a potential new lean meat-boosting feed additive because it can promote animal muscular mass growth and decrease fat accumulation. A competitive colloidal gold-based lateral flow immunoassay system with a portable strip reader was successfully developed for rapid quantitative detection of CLP residue in swine urine. The detection system was optimized so that the detection can be completed within 9 min with a limit of detection of 0.15 μg · liter(-1). The assay exhibited good linear range from 3.0 to 20.0 μg · liter(-1), with reliable correlation of 0.9970 and with no obvious cross-reaction with five other β2-agonist compounds. Twenty spiked swine urine samples were tested by lateral flow immunoassay and liquid chromatography-tandem mass spectrometry to confirm the accuracy of the system. Results show good correlation between the two methods. This method is rapid, sensitive, specific, and convenient. It can be applied in the field for on-site detection of CLP in urine samples.