A preconcentration and determination method was developed for vitamins B1 (thiamin) and B2 (riboflavin) at trace amounts based on cloud point extraction (CPE) and HPLC analysis. As a new approach in this method, Ag(I) ion was used to increase the transferring of vitamin molecules to micelle medium. Then, the formed complexes between Ag(I) ions and vitamins were easily extracted to nonionic surfactant phase. Following phase separation by centrifugation, aqua phase was separated and then surfactant-rich phase was diluted with 300 mu L of 0.1 M HCl in 50% methanol. Under the optimized conditions, linear calibration curves were obtained in the range of 4-400 ng mL(-1) for thiamin and 1-500 ng mL(-1) for riboflavin. The detection limits of method were calculated as 1.33 and 0.35 ng mL(-1), respectively. The relative standard deviations were 2.90 and 2.20% for five replicate measurements at 100 ng mL(-1) concentration level. The method was validated by the analysis of three certified reference materials (NIST 3280, BCR-485, and ERM-BD600) and recovery test. Finally, the method was applied to the determination of vitamins B1 and B2 in real samples, including baby foods, milk, and cereals.