The court ruled against a complaint by several activists and journalists that the decree was illegal and aimed at preventing any information about Russia's military role in eastern Ukraine from being made public.
Signed by President Vladimir Putin in late May, it adds "military losses during war time and during special operations in peace time" to the types of information that constitute a state secret.
Russia's independent media, opposition activists and rights lawyers have been piling evidence of troop losses over the past year but reports of secret funerals and grieving families have been kept out of state media and rejected by the government.
He said that he and other co-complainants had tried to press the Kremlin administration in court to explain what constitutes a "special operation" but the judge let the matter slide.
Leviyev earlier this year said he tracked down Russian soldiers who were killed in eastern Ukraine through social media and published pictures of some of the graves.
Russian authorities have rejected any reports and allegations of its regular army being involved in the conflict between Kiev and the pro-Russian separatists who declared independence in a part of the east.
Ukraine's SBU security service say they have several Russian officers in custody, including members of the GRU military intelligence.
