On September 20, 1999, the Ms7.6 Chi-Chi earthquake ruptured the Chelungpu fault in central Taiwan. In this work, the seismic efficiency, η, which is the ratio of seismic radiation energy, ES, to strained energy, ΔE, of the earthquake is estimated. The value of ΔE estimated from the slip distribution inferred by Dominguez et al. <2003> is 3.208 ¿ 1024 ergs. Based on this value, the η calculated from ES, measured from near-field seismograms and from near-field and teleseismic data are 0.137 and 0.262, respectively. The two values do not seem to agree with the η $leqq$ 0.06 hypothesis proposed by McGarr <1994>. From the ES calculated from two ES-Ms laws, η = 0.049 and 0.019, which fit the hypothesis. However, the two laws could underestimate ES.