Women's apparel company Bebe Stores Inc on Thursday posted a 21.5 per cent year-on-year plunge in first quarter net earnings to $5.1 million amid flat sales.

The California-based operator of 173 stores in the US and Canada said quarterly sales were flat at $73.8m and same-store sales slid 10.3 per cent.

"First quarter sales performance fell below expectations primarily as a result of lower average retail selling prices. As we transition to a more sophisticated assortment, we anticipate price point comparisons to improve," CFO John Kyees said in a statement.