Using a panel of 83 firms for Chemical Biotechnology industry in Taiwan during a 5-year period (2007-2011), this study tests whether there is an optimal level of firm size, which affect R&D and firm performance. The results show that the greater the firm size, the higher will be the firm performance affected by the R&D expenditure. The results allow investors to more accurately value the firm by permitting the R&D expenditures level to serve as a signal.