Abstract: Mitotic index and frequency of chromosomal aberration of root tip cells of wheat seedlings were used as indexes to study the protective effects of lanthanum (La) on wheat seedlings cultured under water planting with heavy metal (Cd) stress. The results show mitotic index decrease and frequency of chromosomal aberration increase under Cd stress, the higher Cd concentrations, and the longer treatment durations, the stronger repression effects. The poisonous effect of Cd on root tip apparently appearing as brown spots and twisted roots induces growing stagnation and abnormal cell chromosome behaviors, including chromosome lag. La can protect wheat seedlings from Cd stress by increasing mitotic index and decreasing frequency of chromosomal aberration, especially reducing formation of micronuclei in root tip cells.