In most plant families, boron (B) is phloem immobile. For plants such as peanut which bury their fruit, the mechanism for B delivery and the B source for fruit and seed growth remains enigmatic. Therefore, this study aimed to establish evidence of B retranslocation in peanut and to identify its importance in plant development. In a sand culture experiment, the increase in B contents in new organs after B withdrawal and the corresponding decline in B contents in older organs was evidence of B redistribution. In a foliar ¹⁰B experiment, the ¹⁰B abundance of treated-leaves decreased and ¹⁰B was detected in leaves and flowers formed after the application of foliar B. Application of ¹⁰B to the roots for a period also provided evidence for the retranslocation of ¹⁰B accumulated during the first growth period. The ¹⁰B abundance in older plant parts declined and ¹⁰B appeared in new organs (flowers, pegs, leaves) that had developed after the ¹⁰B supply had been replaced by ¹¹B. In the fourth experiment, foliar application of B reduced hollow heart, a symptom of B deficiency in seeds, in cv. TAG 24 from 39 to 8% and in Tainan 9 from 63 to 18%. These experiments all provide evidence for B retranslocation in peanut, but further work on the relative importance of the xylem and phloem pathways for B loading into the fruit is needed.