The smut fungus (Ustilago maydis) is a ubiquitous pathogen of corn. One of the symptoms of infected sweet corn by corn common smut is chlorosis on the leaves, so it is especially important to examine how the infection influence the leave chlorophyll content of different hybrids. Five sweet corn hybrids were investigated in the randomized small block field experiments. Hybrids were inoculated by injecting sporidial suspension in the stem, so to induce a high incidence of common smut of corn caused by Ustilago maydis. Two weeks after the inoculation the relative chlorophyll content was measured on seven leaves of different ages per plant by SPAD-502 chlorophyll meter. Because of the infection the relative chlorophyll content of younger leaves was decreased in comparison to the leaves of untreated control plants. The disease systematically spread within the plant causing chlorosis mainly on younger leaves.