This study investigated lead adsorption by carboxylated alginic acid and its application in cleansing cosmetics. Carboxylated alginic acid showed the highest lead adsorptivity after oxidation in a 4-6 mM hydrogen peroxide solution at $20-30^{circ}C$ for 30-40 min. Carboxylated alginic acid adsorbed $648.1{pm}2.8-653.0{pm}2.9$ mg/g of lead dry mass at pH 4-6. Carboxylated alginic acid modified by hydrogen peroxide and potassium permanganate adsorbed $651.3{pm}3.8$ and $639.9{pm}4.0$ mg/g of lead dry mass, respectively. Carboxylated alginic acid showed higher lead adsorptivity after modification by hydrogen peroxide than by potassium permanganate, with an increase of ~30% compared with raw alginic acid. To access the potential application of carboxylated alginic acid in cleansing cosmetics, we investigated the lead adsorptivity, conditions of the cosmetics procedure, and cytotoxicity of various concentrations of cleansing cosmetics added to 5% carboxylated alginic acid. The ideal cosmetic concentrations combined with 5% carboxylated alginic acid were 70% for peeling gel, 20% for massage cream, 20% for foam cleansing and 40% for cleansing cream. There was no cytotoxicity in cleansing cosmetics combined with 5% carboxylated alginic acid.