Fruit flies (Diptera: Tephritidae) are very dangerous insect pests for several horticultural crops causing deleterious quantitative and qualitative reduction in crops. Experiments under field conditions were conducted to determine the population dynamics of both Bactrocera zonata (Saund.) and Ceratitis capitata (Wied.) in guava orchards at Qualyubia Governorate for two successive years. Competitiveness between the two species of fruit flies on guava fruits was also studied. Results indicated that the attracted males of both B. zonata and C. capitata differently fluctuated on guava trees during the first and second years of investigation. During the first year, the highest two peaks of B. zonata of 53.33 and 86.67 individuals/trap/day occurred on the 14^th of June and on the 8^th of November 2021. However, the highest two peaks of C. capitata (148.67 and 219.00 males/ trap/day) were observed on the 11^th of October and on the 8^th of November 2021. During the second year the highest two peaks represented as FTD (Flies/Trap/Day) were 62.00, 55.00 for B. zonata and 153.00, 191.67 for C. capitata; and were recorded on the 26^th of September, the 24^th of October and on the 21^st of November, the 19^th of December 2022, respectively. The population of the two species highly increased throughout guava fruiting seasons. The grand total of the Mediterranean fruit fly was comparatively much higher than that of the peach fruit fly during the two years of investigation. On the other hand, B. zonata failed to compete C. capitata to infest guava fruits throughout the two seasons of investigation.