We propose a nondestructive or optical method of measuring the chlorophyll content in a leaf after constructing a mathematical model of reflectance and transmittance of plant leaves as a function of their chlorophyll pigment content. The model is based on the Kubelka-Munk theory and involves the modeling of the multiple reflection of light in a leaf that is assumed to be composed of a stack of four layers. It also includes the assumption that the scattering coefficient and the absorption coefficient of the Kubelka-Munk theory can be expressed as a linear function of the pigment content of a plant leaf. In the proposed method, the chlorophyll content is calculated from reflectances and transmittances at three bands whose center wavelengths are 880,720, and 700 nm. Experiments were performed to confirm the applicability of the model and the method. Reflectance and transmittance calculated with the model showed good agreement with measured values. Furthermore, several unmeasurable constants necessary in the calculation were determined by a least-squares fit. We also confirmed that these results were consistent with several well-known facts in the botanical field. The method proposed here showed a small estimation error of 6.6 microg/cm (2) over the 0-80 microg/cm(2) chlorophyll content range for all kinds of plant tested.