The Scottish Government responded in full to less than four in 10 of the requests it received under Freedom of Information legislation, according to data gathered by the Tories.
The party found that one in five responses between January 2016 and January 2017 were also late.
The figures put the Government's performance below that of the national average for public sector bodies in Scotland, the Scottish Conservatives said.
Their data showed that 38% of the 2,310 requests submitted to Scottish ministers during the time period resulted in "full disclosure".
All public bodies - including councils and health boards - received 81,641 requests, issuing full responses for 46,486, a total of 56.9%.
The Government was late with its response in relation to 500 of the requests or 21.6%, compared with the national average of 9.6%.
The Tories will use their debating time at Holyrood later today to raise the Government's record on FoI and call for an independent inquiry into the way that it deals with requests.
Tory MSP Jamie Greene said: "These figures prove that the SNP government is paying lip service to the idea of transparency.
"In its place, we see a culture of secrecy where the first instinct is to sweep legitimate requests for information under the carpet.
"These figures will add to the growing question marks over the politicisation of the Scottish Government under the SNP."
He added: "We need ministers to show some humility for once, accept there needs to be a root and branch change in their working practices, and deliver the kind of open government that people want and deserve."
The Government has announced it will publish all information released in response to FoI requests online from July 3.
The Freedom of Information (Scotland) Act gives everyone the right to ask for any information held by a Scottish public authority, with a response required within 20 working days.
Some information can be exempt, however an organisation must explain the exemption which applies.
A Scottish Government spokesman said: "Scotland has the most open and far-reaching freedom of information laws in the UK. We take our responsibility for FOI seriously and in the large majority of cases we respond on time and in full.
"At the same time, the increasing volume and complexity of some requests can prove time consuming, and has the potential to seriously impact on the work of government. The number of FOI requests we receive has been steadily increasing, with more than 2,000 requests last year and more received in the first three months of this year than in the whole of 2007.
"Our FOI legislation is widely recognised as being robust and a recently published report from the former Scottish Information Commissioner noted that Scotland was ahead of the international field in this area.
"Scottish Government records are maintained in accordance with all relevant records management legislation and practice. All Scottish Government guidance on responding to information requests is in the public domain."
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