The United States and its allies have accused the Moscow-backed Syrian regime of being behind the attack, a claim Russia rejects.
"We must state that (the report's) findings are still based on rather questionable data," the foreign ministry in Moscow said in a statement.
"It is not surprising that the contents of the report by the special mission of the OPCW are in many ways biased, which suggests that political motivation is present in the actions of this organisation."
The report did not assign blame for the attack that killed at least 87 people including many children.
More From This Section
US President Donald Trump launched a retaliatory cruise missile strike days later against a Syrian airbase from where it said the chemical weapons attack was launched.
The French foreign ministry said Friday in a statement that the OPCW report "concludes without doubt that sarin... was used in the attack on Khan Sheikhun" and that its findings were "undisputable."
Russia has suggested that rebel fighters were implicated in the attack and that the West is using it as an excuse to push for regime change in Syria.
It also criticised the OPCW for not sending experts to the site of the attack and vetoed a Western-backed UN resolution demanding that the Syrian government cooperate with an investigation.
The foreign ministry said it will "examine the report in detail" and give its full evaluation on July 5.