This study was performed to examine the effect of the clay mineral illite on the improvement of soil and plant growth. Red pepper (Capsicum annuum L.) was used as a test vegetable crop. The experiment was performed during six weeks in the plantation of the Chungbuk National University. Its seedlings were cultivated in the soil normally used for horticultural purpose. Among the seedlings germinated the healthy and regular size of seed were selected and cultivated in the plantation. They were treated with two forms of illite, particulate (PA) and powder (PW), at the following application rates: standard application[P1 (PA1, PW1), soil: illite = 1:20 (w/w)] and two times [P2 (PA2, PW2), 1:10 (w/w)] of standard application. Untreatment (P0) was used as a control soil. At six weeks of cultivation, their growth lengths were correspondingly increased as the application rate was increased ranging from P0, P1, and P2. Their growth length was a little greater with the application of powder illite (PW) than with the particulate illite (PA). Based on the plant analysis of root, leaf, and stem of red pepper, the uptake amounts of K, Ca, and Mg, were correspondingly increased, as the application rate was increased ranging from P0, P1, and P2 respectively. At the same application rate, their amounts taken up in the respective parts were higher with the application of PW illite than on the PA one. Especially the amounts of Ca and Mg were higher in the stem and leaf than root. Consequently, it appears that the illite treatment, especially, PW form of illite, enhance the growth of red pepper in the plantation during the six weeks of experiment.