This review article aims to study the types of seaweed that can be processed into agar, agar extraction methods, characteristic of agar, and application of agar as a food additive. Based on articles and other literature reviews, it can be concluded that: 1) The types of seaweed that can be extracted into agar-agar are Gracilaria sp., Gelidium sp., and Gelidiella sp. 2) Extraction of agar from seaweed can be done using the methods of Yolanda and Agustono [1], Wicaksono et al. [2] and Shantika et al. [3]. 3) The characteristic of agar can be reviewed from particle size, moisture content, ash content, heavy metals, pH, solubility, turbidity, gel strength, and viscosity. 4) Agar-agar as a food additive had been applied to analog rice, jelly drink, and edible film making.