The removal of Pb(II) and Cu(II) ions by using marine red macroalgae (Gracilaria changii) as a biosorbent material was evaluated through the batch equilibrium technique. The effect of solution pH on the removal of metal ions was investigated within the range of 2-7. The response surface methodology (RSM) technique involving central composite design (CCD) was utilised to optimise the three main sorption parameters, namely initial metal ion concentration, contact time, and biosorbent dosage, to achieve maximum ion removal. The models' adequacy of response was verified by ANOVA. The optimum conditions for removal of Pb(II) and Cu(II) were as follows: pH values of 4.5 and 5, initial concentrations of 40 mg/L, contact times of 115 and 45 min, and biosorbent dosage of 1 g/L, at which the maximum removal percentages were 96.3 and 44.77, respectively. The results of the adsorption isotherm study showed that the data fitted well with the Langmuir's model for Pb(II) and Cu(II). The results of the adsorption kinetic study showed that the data fitted well with the pseudo-second order model for Pb(II) and Cu(II). In conclusion, red alga biomass exhibits great potential as an efficient low-cost sorbent for removal of metal ions. © 2019 by the authors.