The objective of this study was to obtain the optimal medium for callus induction
from thallus explants of  Kappaphycus alvarezii (Doty) Doty. Before cultured,  Cottonii
seaweeds collected from the Natuna Islands (Riau Islands Province) were acclimatized in
greenhouse and in semi-sterile culture in the laboratory. Sterilized explants were cultured
on PES and CW media solidified with 0.8% Bacto agar. In each of these media were added
two combinations of plant growth re gulators i.e. BAP+IAA and BAP+NAA. The
concentrations of BAP used were 0, 0.5, 1 mg/l, the concentrations of IAA were 0, 2.5, 5
mg/l, whereas the concentration of NAA were 0,  0.5, 1 mg/l. The result indicated that  the
optimal medium for callus induction was PES solidified medium supplemented with BAP
1 mg/l. Types of callus formed were (a) white compact callus, (b) white filamentous callus,
(c) greenish / brownish callus. Regeneration of callus into clump of filament had  been
done by subcultured the callus into PES solidified medium supplemented with BAP 1 mg/l
+ IAA 2.5 mg/l.