The supermarket apologised and said incidents of mould were "very rare" but could occur as the result of an extremely small hole in the pack.
Lidl customer Richard Leech had previously taken to Twitter to complain to the retailer that his wife was reduced to "uncontrollable vomiting" after they found what they believed was a dead mouse in the rice.
Mr Leech tweeted a picture of the Golden Sun microwaveable pilau rice, which included a grey-coloured substance.
He asked Lidl via Twitter "if you could let me know how this mouse got into my packet of rice?", adding that his house stank of cooked mouse and his wife was suffering from "uncontrollable vomiting" as a result.
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A Lidl spokesman said: "It is never our intention for a customer to be dissatisfied in any way, and we were extremely sorry to see that this particular product did not meet the high standards that both we and our customers expect.
"Following contact with the customer, the matter was immediately escalated to our quality assurance team who, through their initial investigation with the supplier, were able to identify the foreign substance as mould. Whilst very rare, this can occur as a result of an extremely small hole in the pack.
"We only ever work with reputable accredited suppliers who have extensive controls and procedures in place to verify the quality of products. We are, therefore, very disappointed that our expected high standards were not met on this occasion, and are in ongoing contact with the customer on the matter."