Copper(II) ions immobilized onto a biopolymer (sodium alginate) is an effective heterogeneous catalyst for 1,3-dipolar cycloaddition of alkynes with azides and oxidative coupling of 2-naphthols and phenols in water to afford the 1,4-disubstituted 1,2,3-triazoles and biaryl compounds respectively in good yields. The catalyst was recovered quantitatively by simple filtration and reused for several times without significant loss of activity.