This study found that high ferric ion (Fe3+) concentrations lead to high poly-γ-glutamic acid (γ-PGA) production and low-molecular-weight γ-PGA. In cultures containing 7.4mmol/L FeCl3, the average molecular weight of γ-PGA reached 3.18±0.3×105Da, which is a 76% decrease from that in the culture without FeCl3 (1.31±0.14×106Da). Cultures containing increasing concentrations of FeCl3 (0–7.4mmol/L) showed a corresponding increase in γ-PGA yield from 26.57±1.64 to 34.93±1.05g/L. Transcription level analysis indicated that high FeCl3 concentrations could enhance the expression of γ-PGA synthetase genes (pgsA, pgsB, and pgsC), which may contribute to the improved production of γ-PGA. In addition, γ-PGA degradation genes ggt (encoding γ-glutamyltransferase) and cwlO were found to contribute to a lower γ-PGA molecular weight in cultures containing 7.4mmol/L FeCl3. The result of γ-glutamyltransferase activity was in agreement with the results of the transcription level analysis. Overall, this study would provide a novel method for the regulation of synthesis of γ-PGA with low molecular weight.