Alginic acid fiber was used as a novel adsorbent to remove methylene blue from aqueous solution, and adsorption mechanisms were investigated. System variables, including contact time, pH, temperature, and initial concentration were examined to investigate the effect on adsorption in batch experiments. The results showed that equilibrium reached in less than 20 min and pH significantly influenced the equilibrium value. Langmuir, Freundlich, and Temkin isotherm models were employed to analyse the isotherm behaviours. It was found the isotherm behaviours conform to Freundlich and Temkin models well, indicating a chemisorption process. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were employed to investigate kinetic behaviours. The kinetic behaviour is best described by pseudo-second-order model. Thermodynamic parameters indicate that the process is spontaneous and exothermic.