An assessment was made of the antifungal and immunomodulatory activity of dispersions of chitosan nanoparticles obtained by fractional precipitation at pH 5.0 and pH 7.5 using chitosan of different molecular weights. The dispersion of nanoparticles obtained at pH 5 has increased fungistatic activity against C. sativus and A. solani, due to the higher availability of amino groups in looser nanoparticles. This dispersion showed immunostimulating activity, increasing the resistance of wheat to dark brown spot. It was also established that the elicitor activity of dispersions of chitosan nanoparticles is significantly higher than the activity of solutions of the original polymer.