DESCRIBED IS A PROCESS FOR PREPARING 2-TRANS-4-TRANS SORBIC ACID FROM PURE METHYL 2-CIS-5,2-TRANS-5,3-TRANS-5, HEXADIENOATE OR FORM MIXTURES THEREOF. THE PROCESS IS CHARACTERIZED BY THE FOLLOWING STEPS: METHYL HEXADIENOATE IS DISSOLVED IN METHANOL, USING 0.5 TO 1 PART OF METHANOL PER 1 PART OF ESTER; SOLID SODIUM HYDROXIDE IS ADDED IN AMOUNT FROM 0.5 TO 3% BY WEIGHT IN RESPECT OF THE ESTER AND THE WHOLE IS AGITATED AT 20-40*C. FOR 60-120 MINUTES (STEP A); SODIUM HYDROXIDE IS ADDED IN STOICHIOMETRIC AMOUNT FOR THE SAPONIFICATION AND THE WHOLE IS HEATED TO 60-80*C. FOR 60-120 MINUTES UNDER STIRRING (STEP B); WATER IS ADDED IN AMOUNT FROM 0.5 TO 1.5 VOLUMES OF WATER PER VOLUME OF SOLUTION IN ORDER TO DISSOLVE THE SALTS, AND THE METHANOL IS DISTILLED (STEP C); THE SOLUTION IS ACIDIFIED TO PH OF 3.5 WITH 5-15% SULFURIC ACID (STEP D); AFTER FILTRATION AT BETWEEN 30 AND 40*C. (STEP E), THE FILTER CAKE IS WASHED WITH WATER AND WITH AQUEOUS METHANOL (STEP F) THUS OBTAINING 2-TRANS-4-TRANS SORBIC ACID, WITH A PURITY HIGHER THAN 99%.