In this paper, a new hyperchaotic system is constructed by introducing an additional state variable into the third-order Lorenz system. Some basic properties, including dissipativity, equlibria, stability and Hopf bifurcation, of this hyperchaotic system are analyzed in detail, and the bifurcation routes to hyperchaos from periodic, chaotic evolutions are observed. The existence of hyperchaos is verified with Lyapunov exponent spectrum. Moreover, an analog electronic circuit is designed, and various hyperchaotic attractors of this system are observed from the circuit experiments.