Like-for-like sales down 0.8% in May, with homewares and discretionary items down on a year ago.
The like-for-like drop is compared with May 2009, when sales had fallen 1.2% - the worst performance for almost nine years.
Total sales in May were up 2.4% on last year when they had risen 2.7% and non-food was up 2.1%.
The figures, revealed in the latest SRC-KPMG Scottish Retail Sales Monitor found that clothing and footwear enjoyed some sun-driven growth but homewares remained lower than a year ago, with discretionary items worst affected, despite further discounts and promotions.
It was a different story south of the border, where like-for-like sales in the rest of the UK
returned to growth, up 0.8% on May 2009. The Scottish Retail Consortium (SRC) attributes the decline in Scotland to a sharper fall in consumer confidence than in the rest of the UK, with greater concern about public sector job cuts and shoppers more cautious about spending.
SRC head of media Richard Dodd said: "After the distortions caused by Easter, May's results give us a clearer indication of the underlying weaknesses of Scottish sales growth. It's back in line with the poor performances seen in the first two months of the year and below the growth seen in other parts of the UK.
"Fears about public spending cuts are having a bigger effect in Scotland and consumer confidence has slipped further than elsewhere. Customers are nervous about the future and generally reluctant to spend when they don't have to.
"Where there has been growth, it came mainly from non-food goods, clothing and footwear in particular, and was helped by discounts and better weather."