The objective of this study was to identify the changes of certain toxic compounds in some leafy vegetables, which commonly consumed in Upper Egypt. Spinach contained the highest concentration (3837.5 ppm) of nitrate while coriander leaves had the lowest value (575.28 ppm). Nitrite content was higher in cabbage leaves (95.85 ppm) than other leafy vegetables. Spinach and chard leaves contained the highest levels of oxalate (40.11 and 42.38 mg/g "DW", respectively) than other fresh vegetables. Ordinary cooking process led to a significant loss of nitrate and nitrite contents of leafy vegetables under study. The losses of nitrite content were 74.12, 35.13 and 74.12% of its initial values in spinach, cabbage and green Jew's mallow, respectively. However, the loss of oxalate in cooked leafy vegetables varied from 33% in spinach to 100% in cabbage of its initial raw material values. Effect of blanching and freezing on nitrate, nitrite and oxalate contents of some selected leafy vegetables investigated. The loss of nitrate as result of blanching and freezing processes was: 42.3, 49.1 and 54.6% of its initial values in spinach, cabbage and Jew's mallow, respectively. From the obtained results, it could be observed that the highest loss of oxalate was recorded in blanched frozen cabbage leaves which reaching 100%, followed Jew's mallow by 58% and spinach by 30% of its initial values.