Investigators launched a criminal case after two lawmakers claimed they had been publicly insulted, the Investigative Committee said.
"According to investigation, in May-June 2013, unknown people published materials containing public insults to State Duma deputies Yelena Mizulina and Olga Batalina on the Internet," the committee said.
"Besides, false data connected to Mizulina's professional activity were deliberately distributed," it said.
The committee added that investigators are currently trying to establish the perpetrators.
Earlier Russian media reported that Mizulina and Batalina asked prosecutors to launch a criminal case over offensive remarks about them on the Internet.