Proms and Prosecco in the Park and Fireflies Festival would have taken place at Weston Park across May 26 and 27, and would have included performances from Belle Voci, Charlie Green, the Darby Singers and David Lane.
But organisers Fizz Festivals said ticket sales had been lower than expected and that they had taken the difficult decision to cancel.
Those who had already bought tickets will be contacted to arrange a refund or tickets for another Fizz Festivals event.
Esther Wright, who put together the event, said: "It is with great regret that we have taken the decision to cancel Proms & Prosecco in the Park at Weston Park and Fireflies Festival on May 26 and 27.
"Unfortunately, ticket sales didn't reach a sufficient level to be able to go ahead with these events and we have taken the decision to cancel. This has been an incredibly tough decision.
"Fizz Festival's events have had a happy, family vibe, with all generations enjoying a day of live music, great food and drink, in a friendly community atmosphere. We need a sizeable audience to create that fizzy vibe and that hasn't happened this time.
"All ticket holders will be contacted by Fizz Festivals' ticketing partner to arrange a refund on their tickets or the opportunity to transfer their booking to another Fizz Festivals event.
"Fizz Festivals and Weston Park will be continuing to work together on future events and we look forward to sharing details of these in due course."
The annual Proms & Prosecco in the Park at Chetwynd Deer Park in Newport will still go ahead on September 14.
The event will again give families the chance to set out their picnic blankets and settle in for six hours of live music, activities for children and food stalls.
Now in its third year, tickets are now available. Entry costs £26 until July 14, and then rises to £30.Children under 10 can enter for free.
For more information visit fizzfestivals.com