Abstract: ObjectiveEffects of ultrasound combining modified atmosphere package(MAP) on preservation quality and physiological changes of Psidium guajava fruits were studied in order to provide reference for its postharvest storage tech-nique. MethodUsing Zhenzhu P. guajava as experiment material, the quality and physiological indexes of three groups were determined once every six days during postharvest storage at ambient temperature(5-15 ℃, relative humidity 70%-85%). The fruits were treated with ultrasound(frequency 40 kHz, output power 360 W) for 5 min or 10 min combined with MAP after drying. The fruits being soaked in distilled water for 5 min and no bag were taken as control group(CK).ResultThe nutritional quality, phenylalanine enzyme(PAL) activity and total moisture of P. guajava was well main-tained with ultrasound combining MAP. Respiratory intensity, cell membrane permeability and peroxidase(POD) activity of P. guajava fruits were restrained, and senescence was delayed. Ultrasonic treatment for 10 min combining MAP presented the optimal preservation effects. After 30 days storage, good fruit rate reached to 81.82%, weight loss rate was only 1.11%, contents of chlorophyll, protein and vitamin C, PAL activity were higher than those of CK on day 18, deformation degree, POD activity, cell membrane permeability and respiration intensity were superior than those of CK, and the storage longevity prolonged 12 days than that of CK. ConclusionUltrasound combining MAP can reach good preservation effects on P. guajava fruits. It prolongs storage longevity and keeps the original flavour of the fruits. The best preservation method is ultrasonic treatment for 10 min, which can be used for P. guajava fruits postharvest preservation.