A range of phosphonium ionic liquids having the generic formula [PR 3 R9]X (R and R9 are alkyl groups; X is halide, trifluoromethanesulfonate, bis(trifluoromethylsulfonyl)imide, nitrate, dialkylphosphinate, dicyanamide, decanoate, tetrafluoroborate, hexafluorophosphate, or diisobutyldithiophosphinate have been prepared, characterised, and tested for anti-microbial activity and anti-electrostatic properties. Within this group of phosphonium salts, in contrast to their 1-alkyl-3-methylimidazolium analogues, both cation structure and the type of anion have effects on their biological activity. The ionic liquids also showed high anti-electrostatic effect.