The effect of five different NaCl concentrations, namely 3.5, 6.5, 9, 12 and 15 g/l NaCl on PHA productivity using Cupriavidus necator has been investigated alongside a control (no added NaCl) when acetic acid was used as the sole carbon source. A dielectric spectroscopy probe was used to measure real-time PHA accumulation online in conjunction with the chemical offline analysis of PHA. The highest PHA production was obtained with the addition of 9 g/l NaCl, which yielded 30% higher PHA than the control. Increasing the addition of NaCl to 15 g/l was found however to inhibit the production of PHA. NaCl addition can be used as a simple, low cost, sustainable, non toxic and non reactive external stress strategy for increasing PHA productivity when compared to previous increased temperature and other types of chemical stress such as ethanol, hydrogen peroxide or metal stress. The order of PHA accumulation for the above salt concentrations were 9 g/l > 6.5 g/l > 3.5 g/l > control > 12 g/l > 15 g/l NaCl, which clearly indicates that addition of NaCl, which up to 9 g/l enhanced PHA production.