The effect of the interaction between inoculation of Cucumber mosaic virus (CMV) and Tomato mosaic virus (ToMV) in tomato plants were demonstrated for symptom severity, plant height, leaves number, chlorophyll content and relative virus concentration. Symptoms assessed after 15 and 30 days of inoculation were affected with double inoculation by both viruses. Tomato plants co infected with CMV then ToMV after 7 days caused high increase in the symptoms severity. All inoculations reduced the stem height as well as number of leaves and chlorophyll content but with different percentages. The greatest reduction in stem height, leaves number and total chlorophyll content were 47.54, 37.93 and 53.93%, respectively when tomato seedlings were inoculated first with CMV and 7 days later with ToMV. Relative virus concentration was determined by indirect ELISA. As compared with the corresponding positive controls, simultaneous infection with CMV and ToMV significantly decreased relative concentrations of both viruses. The highest increase in relative concentration of CMV was 33.41% obtained when the plants were inoculated with ToMV first and CMV, 7 days later. While, combined infection with CMV first and ToMV, 7 days later resulted in higher increase of ToMV by 35.12 %.