MILAN, Dec 23 (Reuters) - An Italian judge on Thursday dropped a case against the CEO of Unipol and six other people related to the 2013 merger between Italy's second-largest insurer and smaller rival Fondiaria-SAI, a judicial document seen by Reuters showed.

Carlo Cimbri and the others were under investigation for alleged market rigging as Milan prosecutors suspected Unipol did not accurately account for its large structured derivatives portfolio and that this had an impact on the setting of the share swap ratios for the tie-up with Fondiaria.

At the end of the investigation, however, the public prosecutor's office itself asked for the case to be dismissed.

Milan judge Anna Calabi, in the decree filed on Dec. 23 and seen by Reuters, granted the requests of prosecutors and dropped the case against Cimbri and the other suspects, saying there was no crime.

Unipol declined to comment.

Bologna-based Unipol agreed to buy troubled rival Fondiaria in 2012 in a complex rescue operation that was held up by a series of regulatory and legal hurdles.

The merger created UnipolSai, Italy's second largest insurance group behind Assicurazioni Generali, and was officially completed on Jan. 6, 2014. (Reporting by Alfredo Faieta Writing by Emilio Parodi Editing by Gianluca Semeraro and Mark Potter)