The adsorption of nicotinic acid molecules from their solution in the aqueous phase was studied in batch mode by using magnetically activated carbon (M-AC) as the adsorbent. Activated carbon was magnetized by a coprecipitation method. The effects of the amount of adsorbent (0.25 to 5 g.L-1), initial acid concentration (2.46 to 14.77 g.L-1 or 0.02 to 0.12 mol.L-1), contact time (0 to 120 min), and temperature (298 to 333 K) on the percentage removal were investigated. Theoretically (from the Langmuir isotherm), an adsorption capacity of 23.28 g.g(-1) was obtained by M-AC for acid removal. Equilibrium isotherms such as the Langmuir, the Freundlich, and the Temkin were applied to determine equilibrium parameters and to fit the equilibrium data, out of which the Langmuir gave the best match to the results. Nicotinic acid adsorption kinetics was modeled with pseudo-first order, pseudo-second order, and intraparticle diffusion models. The kinetic data was best described by the pseudo-second-order model. Thermodyn amic parameters such as Delta H degrees, Delta S degrees, and Delta G degrees were calculated, and their values pointed out that the adsorption of acid molecules onto M-AC was exothermic and the process was spontaneous.