Abstract: Melee-size synthetic yellow diamonds have appeared in the gem market, as loosestones or mountedin jewelries. Recently, the authors found that there were several HPHT synthetic yellow diamonds among 263 pieces of yellow diamonds mounted in an emerald-diamond ring during the conventional gem testing. In order to distinguish synthetic diamonds from natural counterparts in the diamond jewelries, the systematic investigation was performed for the mounted melee-sized yellow diamonds, by using ultraviolet fluorescence, DiamonView^TM, micro-infrared spectroscopy, photoluminescence spectroscopy, etc. The results showed that 7 pieces of melee-sized yellow diamonds are HPHT synthetic diamonds, all of them are pure type Ib, with ignorable aggregate nitrogen and no hydrogen in the mid-infrared absorption. The natural yellow diamonds are mainly type IaA-Ib and Ib-IaA, with the hydrogen-related absorptionlines at 1 405, 3 107 cm^-1, etc, and single nitrogen related peaks at 1 352, 1 358 cm^-1, etc. Additionaly, the synthetic diamonds have strong and bright green fluorescence, the natural ones have very weak or none. The nickel-related lines at 883, 884 nm in 7 pieces synthetic diamonds could be detected. Therefore, the combination of micro-infrared spectroscopy with fluorescence characteristics is an effective method for rapid and accurate separation of melee-sized natural and synthetic diamonds.