We report in this article a method to tune the sol-to-gel transitions of moderately concentrated aqueous solutions of doubly thermosensitive hydrophilic diblock copolymers that consist of two blocks exhibiting distinct lower critical solution temperatures (LCSTs) in water. A small amount of weak acid groups is statistically incorporated into the lower LCST block so that its LCST can be tuned by varying solution pH. Well-defined diblock copolymers, poly(methoxytri(ethylene glycol) acrylate)-b-poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid) (PTEGMA-b-P(DEGEA-co-AA)), were prepared by reversible addition-fragmentation chain transfer polymerization and postpolymerization modification. PTEGMA and PDEGEA are thermosensitive water-soluble polymers with LCSTs of 58 and 9 degrees C, respectively, in water. A 25 wt % aqueous solution of PTEGMA-b-P(DEGEA-co-AA) with a molar ratio of DEGEA to AA units of 100:5.2 at pH = 3.24 underwent multiple phase transitions upon heating, from a clear, free-flowing liquid (<15 degrees C) to a clear, free-standing gel (15-46 degrees C) to a clear, free-flowing hot liquid (47-56 degrees C), and a cloudy mixture (>= 57 degrees C). With the increase of pH, the sol-to-gel transition temperature (Tsol-gel) shifted to higher values, while the gel-to-sol transition (Tgel-sol) and the clouding temperature (T-clouding) of the sample remained essentially the same. These transitions and the tunability of Tsol-gel originated from the thermosensitive properties of two blocks of the diblock copolymer and the pH dependence of the LCST of P(DEGEA-co-AA), which were confirmed by dynamic light scattering and differential scanning calorimetry studies. Using the vial inversion test method, we mapped out the C-shaped sol-gel phase diagrams of the diblock copolymer in aqueous buffers in the moderate concentration range at three different pH values (3.24, 5.58, and 5.82, all measured at similar to 0 degrees C). While the upper temperature boundaries overlapped, the lower temperature boundary shifted upward and the critical gelation concentration increased with the increase of pH. The AA content in PTEGMA-b-P(DEGEA-co-AA) was found to have a significant effect on the pH dependence of Tsol-gel. For PTEGMA-b-P(DEGEA-co-AA) with a molar ratio of DEGEA to AA units of 100:10, the Tsol-gel of its 25 wt % aqueous solution increased faster with the increase of pH than that of PTEGMA-b-P(DEGEA-co-AA) with a DEGEA-to-AA molar ratio of 100:5.2.