A new chain-extension modifier for bismaleimide (BMI), 2,6-di-(4-aminophenoxy)benzonitrile (DAPB), was synthesized through nucleophilic substitution of 2,6-dichlorobezonitrile by 4-aminophenol using anhydrous sodium carbonate as an acid acceptor, toluene as a dehydrating agent, and N,N'-dimethylacetamide (DMAC) as a dipolar aprotic solvent. Based on the diamine, another modifier for bismaleimide, 2,6-bis(4-maleimidophenoxy)benzonitrile (BMPB), was also synthesized, first by the reaction of DAPB with maleic anhydride and then by dehydration. DAPB and BMPB were used to modify a popular commercial BMI, 4,4'-bismaleimidodiphenylmethane (BMDPM), for improving the shear strength of the resin. The results showed that the shear strength of the DAPB-modified BMDPM resin was superior to that of either neat BMDPM or the 4,4'-diaminodiphenylmethane (DADPM)-modified BMDPM (a commercial modified BMDPM resin system). In addition, the heat resistance of the cured DAPB-modified BMDPM resin was higher than that of the cured DADPM-modified BMDPM resin. The excellent properties were also found in the BMPB-modified BMDPM resin. It was found that the BMPB-modified BMDPM resin was superior to neat BMDPM in both shear strength and heat resistance.