String beans raw，cooked for 5，15 and 30 min. were studied microscopically. It was found that as the time for cooking was increased，the green pigment decreased and substances within each cell tended to loosen and coagulate as compared to the raw bean where the chloroplasts were situated around the periphery of the palisade cells. When cooking was up to 30 min. breaks in the epidermal and parenchyma cells and extreme shrinkage within the endodermis were observed.