Abstract A commercially available bituminous granular activated carbon (GAC) was subjected to thermal treatment with ammonia for 60 min at temperatures of 500–800 °C. The effect of this treatment on the physical and chemical characteristics of carbon was studied in detail. Comparison of virgin and NH 3-tailored carbons relative to pore volume distribution and argon-BET surface area indicated that ammonia acted as an activating agent under these conditions. Micropore volume increased with increasing treatment temperature up to 700 °C; and then declined at 800 °C. Elemental analysis results showed that nitrogen was incorporated into the carbon matrix during the thermal treatment as proven by an increase in N-content from 0.64% for virgin GAC up to 1.61–1.63% for all the tailored samples. The ammonia treatment caused an increase in positive surface charge density over a broad pH range; and this was reflected in a higher pHpzc and pH IEP. This was attributed to the more basic nature of the carbon surface after its treatment in ammonia.