The use of natural and biodegradable material (such as fish flour) counteracts stress as cheaper and safer alternative for toxic chemicals (such as pesticides). The effect of calcium and fish flour (Ca and FF) (single or in combination) to improve plant tolerance against salt stress was studied. Sterilized mentha seeds were imbibed in each treatment: FF (10 g mL(-1)), Ca (1, 3%) applied alone and in Ca+FF-combination shaking for 24 h at 150 rpm. Changes in the antioxidants (carotenoids, phenolic, and flavonoid), enzymatic system (superoxidase - SOD, guaiacol-dependent peroxidase - GPX and phenylalanine ammonia-lyase - PAL) and lipid peroxidation levels of mentha seedlings were investigated under salt stress. It was suggested that Ca and/or FF had positive regulation effects on the key enzyme activities related to phenolic compounds biosynthesis and individual phenolic contents under salt stress. Additionally, the mentha plants developed from Ca+FF-combined pre-treatments showed better response to salinity than either Ca or FF single pretreatment. Suppression of salt injury by Ca+FF pre-treatment reduced the LPO levels, increased enzyme activities and promoted total flavonoid and phenolic contents. Ca+FF-combined pre-treatment of mentha seeds seem to be a reliable, not-expensive and easy procedure to enhance plant salt tolerance and to gain more biomass.