The latent heat storage (LHS) technique is of crucial importance in chemical energy engineering. Inspired by multi-bifurcated fern leaves, a mimic fern-fractal fin is designed to improve the thermal energy charging efficiency. This paper develops a transient melting model of a rectangular LHS unit using fern-fractal fins, and their melting behaviors are compared with the conventional fins. Besides, a parametric optimization of fern-fractal fins is conducted for maximizing the thermal efficiency based on the response surface method (RSM). The results indicate that the temperature uniformity is more superior and the melting duration is shorter for the fern-fractal LHS unit when compared with the conventional one. Interestingly, the fern-fractal LHS device presents a slower heat storage rate during the initial conduction-dominated and early convection-dominated melting stages, while a prominent melting enhancement is achieved during the later melting stage. The shortest melting time is obtained based on the RSM technique when a fern-fractal fin with length ratio alpha = 0.94 and branch angle theta = 54.7 degrees is utilized. Compared with a conventional fin, the averaged heat storage rate increases by 88.3%, and the total melting time is declined by 40.3% for an optimized fern-fractal fin. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.