In the year to 8 September, the brand's market share dropped from 19% to 13%, according to IRI Infoscan.
In comparison, Innocent has grown its share of the sector to 72%, up from 63% last year. The brand has more than doubled its turnover in the past two years, from £37.8m in 2005 to a predicted £100m in 2007.
PJ Smoothies, which has eight flavours, was the first brand to launch in the UK smoothie market in 1994 when founder Harry Cragoe imported the concept from California. The brand, then known as Pete & Johnny's, adopted brand styling similar to Ben & Jerry's retro look.
The brand was subsequently renamed PJ Smoothies and relaunched following its acquisition by PepsiCo in 2005 for a reported £20m. However, its overhauled look did not strike a chord with consumers.
The range was redesigned again this year in an attempt to move closer to the brand's original design simplicity. However, the revamp has received little advertising support and failed to boost sales.
The UK smoothie market is now worth £185m and accounts for 19% of the chilled juice market, according to IRI Infoscan.