Microscopic observations of arbuscular mycorrhizae (AM) were done with the colonizations of AM and the determinations of chitin in the plant roots of Sorghum bicolor, Cassia mimosoides, Capsicum annuum and Allium fistulosum. The intercellular and intracellular hyphae, arbuscules and vesicles were microscopically observed, according to increases of colonization of AM in the roots of four plants. The growth of AM fungi appeared sigmoid with the cultivation days after inoculation. The growth of AM fungi were inversely influenced by the additions of commercial fertilizers, P<N<K, respectively. This growth of AM fungi was speculated to be related to the plant metabolites, but not by the phosphate in the soils. The effects of inoculum of AM fungi were similar to or slightly less than those of additions of commercial fertilizers for plant growths of Capsicum annuum and Allium fistulosum. The effects of AM fungi were, especially, greater in the plants of Allium fistulosum and Cassia mimosoides. This works indicated that the inoculations of AM fungi were better than additions of commercial fertilizers for the plant of Allium fisulosum.