Dramatic changes in mesoscale ordering and macroscopic mechanical behavior are observed in smectic polydomain networks after annealing at a temperature well above the glass transition temperature but below the clearing temperature. Tensile testing reveals gradual stiffening and loss of extensibility, and X-ray linewidth measurements confirm that stiffening is initially due to thickening of domains. At long annealing times, a more highly ordered smectic mesophase forms, further stiffening the networks and reducing their extensibility. Increasing the concentration of (flexible) crosslinkers hinders domain growth and suppresses formation of the higher order mesophase, a useful guideline for design of smectic networks that exhibit reduced sensitivity to thermal history. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013