Abstract: To study the effects of potassium (K) on leaf anatomical structures of different cotton genotypes, a pot experiment was conducted at Huazhong Agricultural University. There were two cotton genotypes (HG103, and LG122), two K application levels (0 and 0.4 g/ kg soil). The HG103 (high K efficiency genotype) and LG122 (low K efficiency genotype) were selected from 86 cotton cultivars (Gossypium hirsutum L.). The results show that the upper leaves main veins of the upper or the lower epidermis cells of HG103 are more tight and neat than those of LG122 when adding K, while the main veins of lower leaves are opposite. The upper leaf main veins of HG103 are better than those of LG122 under the no K level. HG103 has lots of vascular xylem vein catheters which benefits nutrients and moisture transportion, while LG122 has small number of xylem conduits. The phloem veins of the upper part of HG103 are better than those of LG122, which could help HG103 transport much of photosynthetic products. The structures of upper leaf mesophyll cells of HG103 and LG122 are not very different when applying K, but lower leaf palisade tissues of LG122 are more neatly arranged than those of HG103. Under the K insufficiency, upper leaf epidermal cells of HG103 are more orderly, and shapes of palisade and spongy tissues are more regular, while the palisade tissue and spongy tissue of the lower leaves of LG122 are better than those of HG103.