The analytical sensitivity of laser-induced breakdown spectroscopy (LIBS) is significantly influenced by the electronic bremsstrahlung emission in plasma. Since the time duration of the background emission in LIBS is usually shorter than that of the atomic emission, it is possible to get high signal to background ratio by using timeresolved signal detection technique. A gated photomultiplier tube with a simple new gating circuit is applied in LIBS signal detection and the copper impurity in aluminum alloy is analyzed with improved analytical sensitivity. The rejection ratio of the background reaches 15∶1. The limit of detection of copper in aluminum alloy is determined to be 1.02×10^-6 in single-pulse LIBS, which is much lower than that obtained without gating technique. The gated photomultiplier tube can be used to reduce influence of the background emission and will be helpful with improving both analytical sensitivity and spatial resolution of LIBS.