Agar, agarose, and agaropectin were extracted from the red alga Ahnfeltia plicata, and their properties and structures were characterized. Agar was extracted by a comparatively low alkaline consumption of 1.2%. It exhibited a gel strength of 1 152.50±74.25 g/cm2 and a sulfate content of 0.55%±0.08%. The yield of agar from A. plicata was 24.53%, which is higher than those of other agarophytes commonly used in China. Three kinds of the method were compared for the purification of agarose, and the physicochemical properties of agarose that was prepared under the optimal condition were identical to those of commercially available agarose. Furthermore, agaropectin was purified from A. plicata and characterized by GC, HPLC, UV-spectrum, and FI-IR to understand its composition and structure. It was the first time to comprehensively study the agar and its fractions from the red alga of A. plicata. This research provided an eco-friendly agar extraction method from A. plicata and revealed its potential application for the production of agar, agarose, and agaropectin.