Cellulose nanocrystals derived from tunicates (t-CNC) were used as a reinforcing nanofiller for polyimide aerogels. Two sets of polyimide aerogels, containing either 2,2'-dimethylbenzidine (DMBZ) or 4,4'-oxydianiline (ODA) and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) cross-linked with 1,3,5-tris (4-aminophenoxy)benzene (TAB), were studied. Total solids composition of the aerogels were kept constant at 7.5 wt %, with 0-13.33 wt % of the total solids being the carboxylic acid-functionalized t-CNC (t-CNC-COOH) filler. The incorporation of the t-CNC-COOH, with carboxylic acid content of either 560 or 920 mmol/kg, in the polyimide aerogel networks improved both physical and mechanical properties of the final materials. Isothermal aging of t-CNC-COOH aerogel composites was also conducted at 150 and 200 degrees C for 24 h. Higher content t-CNC-COOH/polyimide aerogels showed less change in their density and reduced shrinkage during aging, which further emphasized the effect of the t-CNC-COOH reinforcement in retaining the structural integrity of the aerogel.