The invention relates to a herbicide formulation comprising a water soluble salt of n-phosphomethylglycine and at least one adjuvant, the said adjuvant consisting in an alkoxylated imidazoline with the following structure I wherein R1 is a saturated or unsaturated C4 to C24 fatty acid. The use of the alkoxylated imidazoline provides as a result a herbicide formulation that is not irritant to the skin or the eyes. Furthermore, the adjustment of the degree of ethoxylation or propoxylation of the imidazoline permits the compatibility thereof with the various glyphosate salts, allowing the obtainment of concentrated solutions that maintain stability at temperatures higher than 60° C., without requiring other adjuvants.