The hydrothermal reaction of In 3+ and 1,2,4-benzenetricarboxylic acid with the presence of piperazine leads to the generation of a novel 3D porous coordination polymer, [H 3O][In 2(btc)(bdc)(OH) 2]·5.5H 2O ( 1), (btc=1,2,4-benzenetricarboxylate, bdc=1,4-benzenedicarboxylate). Compound 1 crystallizes in orthorhombic space group Pbca with a=16.216(7) Å, b=13.437(6) Å, c=31.277(14) Å, and Z=8. It is interesting to find that the in-situ decarboxylation reaction of 1,2,4-benzenetricarboxylate (btc) partially transformed into 1,4-benzenedicarboxylate (bdc) occurs. The 16 indium(III) centers were linked by four btc, four bdc and two μ 2-OH ligands to form a box-girder. The adjacent box-girders are further connected by the bdc and btc ligands to generate a novel porous metal–organic framework containing nanotubular open channel with a cross-section of approximately 11.5×11.3 Å 2. The micropores are occupied by lattice water molecules, and the solvent-accessible volume of the unit cell was estimated to be 3658.6 Å 3, which is approximately 53.7% of the unit-cell volume (6815.4 Å 3).