Customer Charlie Peach made the stomach-churning discovering after purchasing a packet of the supermarket chain's own-brand basmati rice from the Walderslade store in Chatham, Kent.
Sharing his findings on Facebook, Charlie uploaded a video which showed the unsettling moment he discovered maggots wriggling around at the top of his opened packet of rice.
In the clip, Charlie zooms into the packet on a countertop and can be heard saying 'What the hell is that?' to which a woman replies 'It's maggots!'
Captioning his clip, he said: 'This is what we were confronted with when we opened a packet of Morrisons home brand rice..... MAGGOTS.
'We have returned the rice complete with maggots to your Walderslade branch and were offered a paltry £30 'gesture of goodwill'.
'This is an absolute insult considering the time taken to return the item and deep clean our cupboards of stray maggots, then purchase a takeaway on the evening we found them, ruining our evening meal.'
Charlie also took aim at the 'disgusting and shameful' customer service he received following the horrifying incident.
He added: 'This coupled with the fact we were charged £12 while kept on hold when contacting Morrisons' head office after several attempts to resolve this issue in branch failed dismally.
'Morrisons detail to customer service is absolutely disgusting and shameful, the retail market is a very competitive one, clearly we need to reconsider where to do our weekly shop.'
A Morrisons spokeswoman said: 'We have apologised to Mr Peach and are investigating the issue. We have offered him replacement products, loyalty card points and £30 as a gesture of goodwill.'
This isn't the first time Morrisons have received complaints over their food.
In December last year they were forced to apologise after a customer discovered maggots in her box of chocolates.