The tie-line and solubility data for the systems containing formic acid (FA), water, and methyl isobutyl ketone (MIBK) + NaCl were determined experimentally at temperature 298.15 K and atmospheric pressure. The effect of salt 0.05-0.15 mass fraction (base on mass of initial water) was investigated. Binary interaction parameters were ascertained by comparing the experimental tie-line data with the nonrandom two-liquid model (NRTL) correlations. The tie-line data of the systems were analyzed using the Othmer Tobias, Hand, and Bachman correlation equations. Separation factors and distribution coefficients were assessed. The results show that enlargement of the two-hase region occurred when the concentration of salt increased in the initial aqueous phase; adding salt to the system proved beneficial in separating FA from water.