The company, Paradigm Genetics, recently teamed up with the German pharmaceutical and chemical company Bayer in a deal which earned it around pounds 26m.
Paradigm will also receive success fees from Bayer if its herbicide-resistant crops are grown commercially.
John Redwood, the Conservative trade and industry spokesman, said the revelation provided further evidence that the minister's position was untenable.
"He is very committed to this technology and has had a very wide range of business interests in it, some of which continue," he said.
"It makes it even more important that he should get his story straight about what he is allowed to do in government."
Lord Sainsbury, the science minister at the centre of a row over genetically modified food, is not directly involved in licensing the products but does sit on a cabinet committee on biotechnology.
Innotech Investments Ltd, a firm funded by Lord Sainsbury but placed in a trust with his other business interests when he became a minister, is named on Paradigm's web site as one of three major investors who put a total of pounds 8m into the company.
The release is dated 1 July 1998 - four weeks before Lord Sainsbury became science minister.
Lord Sainsbury's direct involvement in the biotechnology business comes through two firms - Innotech and Diatech. Innotech owns Floranova, a plant breeding company, and Elite Seeds, a seed and plant distribution company, both of which are based in Norfolk and both of which are developing genetically modified plants. Diatech is directly involved in "natural science engineering".
Lord Sainsbury's charity, the Gatsby Foundation, has put more than pounds 2m a year into the study of plant science since 1990, most of which has been used to set to set up the Sainsbury Laboratory in Norwich.
The laboratory is developing genetically modified crops and is based in the grounds of the John Innes Centre, the biggest genetic research campus in Europe.
Paradigm has a scientific advisory board which includes the head of molecular genetics from the John Innes Centre, Michael Bevan.
Lord Sainsbury has said he will step aside from ministerial decisions on genetically modified food, but is in charge of the overall budget of the Biotechnology and Biological Science Research Council.
The council gives the Sainsbury Laboratory more than pounds 800,000 per year in funding through the University of East Anglia. A spokesman for Lord Sainsbury said he had placed all his interests in a trust as soon as he became a minister.
"The nature of this thing is that he doesn't know if he still owns it and he doesn't have any connections with its current activities," he said.
The Conservative leader William Hague tried to put new pressure on the Government by announcing that his party would introduce a measure in the House of Lords to place a moratorium on GM crops.
The measure would have no chance of success.Reuse content