PURPOSE: To easily obtain the subject compound useful as a cationic surfactant having excellent thermal stability and usable as an antistatic agent or softening agent by reacting a tri(aliphatic hydrocarbon)amine with diethyl sulfate in a specific solvent.

CONSTITUTION: The objective compound generating remarkably decreased amount of volatile substance in the melt-mixing with a synthetic resin can be produced by reacting (A) a tri(aliphatic hydrocarbon)amine such as 16C,18C- mixed alkyl dimethylamine produced by substituting the H of ammonia with aliphatic hydrocarbon groups containing at least one aliphatic hydrocarbon group having ≥4C (preferably ≥8C) long-chain aliphatic hydrocarbon chain with (B) diethyl sulfate especially preferably containing ≤0.2% of water and ≤0.1% of ethyl sulfate and sulfuric acid in (C) an organic solvent containing a halogenated hydrocarbon (e.g. chloroform or CCl4) or ≤20mol (based on 1mol of diethyl sulfate) of an alcohol (e.g. ethyl alcohol or propyl alcohol) at room temperature to 90°C.