Abstract: It is known that treatment with boron may to a certain extent reduce the percentage of boll shedding in cotton plant. It is also known that boron plays a special role in carbohydrate metabolism of the plants in general. The present work attempted to elucidate the effect of boron treatment on the translocation and metabolism of carbohydrates in cotton plant. The first internode of the fourth to the sixth fruiting branch of field grown cotton plant was chosen as experimental material. Only one leaf and one newly-opened flower were left on the branch. Ringing was performed 3 cm below the flower in order to localize the treatment effect. Boron treatment was either applied to the leaf or to the flower. Treatments were either done in the light, or when plants were kept in darkness. At various intervals (24 and 48 hours) after treatment, samples were taken, each sample being constituted of 15 branches. Reducing sugars, sucrose and starch were determined respectively. Experiments showed that starch made up 10%–13% of the dry weight of cotton leaf, it made up 5%–6% of the dry weight of the young boll. Boron treatment of the leaf did not only increase the content of starch and reducing sugars of the treated organ, but also increased the content of reducing sugars of the boll opposite to the treated leaf. When plants were kept in darkness, boron treatment of the leaf increased the content of reducing sugars of the treated leaf at the expense of the content of starch. This treatment caused an increase of both starch and reducing sugars in the boll. It is considered that the beneficial effect of boron on boll shedding is related to its improved carbohydrate supply to the boll.