In recent years the biogenic synthesis of metal oxide nanoparticles using natural resources has received significant attention due to their easy availability, low cost and environmentally benign protocol. In this study, Cu₂O nanoparticles have been synthesised using Syzygium jambos (L.) Alston plant extracts without using toxic chemicals. The average size of the nanoparticles is 7.6 nm which found to have excellent catalytic activity in the ipso-hydroxylation of arylboronic acids without using H₂O₂. Mild reaction condition, excellent yield, easy separation and reusability of the catalyst are the advantages of this method.