To provide a ceiling panel connecting structure and a tightening fitting which prevent formation of a step at the connection between both ceiling panels and eliminate the need for complicated tightening operations.

In this ceiling panel connecting structure, one of two ceiling panels 1, 2 each having a backing material 12 mounted on the back of a plate- shaped element 11 has its plate-shaped element 11 curved at its end toward the back to provide a receiving part 13 which opens laterally; the end of the other ceiling panel 2 is curved toward the back to provide an insertion part 23 which can be inserted into the receiving part; the insertion part 23 of the other ceiling panel 2 is inserted into the receiving part 13 of the one ceiling panel 1 and the ceiling panels 1, 2 are tightened together by a channeled tightening fitting 3 while the insertion part 23 is inserted in the receiving part 13. A bolt 32 which is clamped by the channeled tightening fitting 3 while the insertion part 23 is inserted in the receiving part 13, and which is passed through a through hole 311 bored in one side wall 31 of the tightening fitting 3, has its end threaded into a tapped hole 331 bored in the other side wall 33, to tighten the ceiling panels together while the insertion part 23 is inserted in the receiving part 13.