Polymer gels, defined either from the structural point of view (structural gel) or by their mechanical properties (mechanical gel), are ubiquitous in our daily life. In our previous work U. Phys. Chem. B, 2011, 115, 11345), we reported that, the mechanical gel formed by strong solvophobic ABA block copolymers with fixed chain compositions shows a strong mechanical response, which meant the formed gel had a high modulus. In this work, we focus on the effect of chain composition on the relationship between structural gel and mechanical gel, where the chain length of block copolymer is lower than its entanglement chain length for simplicity. Our results show that the chain composition has a great effect on the mechanical response of the ABA copolymer solutions with a strong solvophobicity. On the other hand, for the structural gel formed by weak solvophobic block polymers, we do not find any strong mechanical responses even we change the chain composition in a wide range. Moreover, we find three typical gelation processes, companied with three kinds of different mechanical responses. These results may provide us an effective method to control the mechanical property of a polymer gel as expected. (C) 2014 Elsevier Ltd. All rights reserved.