Pesticides may remain on the surface of fresh produce due to inappropriate and inadequate cleaning. In view of the public health significance of pesticide residues in fresh produce and the long-term effects of low dose exposure of these pesticides, decontamination procedures are needed for ready-to-eat foods, especially vegetables. Ultrasound cleaning is considered to be an effective environmentally-friendly decontamination process which is unique in its ability to remove pesticides compared to other conventional methods. The reduction of dimethoate and diazinon residues from fresh Chinese cabbage by sequential multi-frequency ultrasound cleaning treatments was investigated in this study to ascertain the levels of reduction after cleaning. The ultrasonic treatment has higher efficiency on the removal of these organophosphorus pesticides compared to ordinary water cleaning. The removal rates of ultrasonic cleaning treatments for dimethoate and diazinon residues were in the range of 20.10–72.42% and 29.60–77.37% compared to the ordinary water cleaning with 13.24–19.89% and 17.32–24.16% respectively. In addition, quality parameters for the leaves treated were also assessed. The physical impairment and vitamin C loss increased with the increase in ultrasonic frequency combination and cleaning time. Application of triple frequency ultrasound and extended washing time resulted in high dimethoate (>70%) and diazinon reduction (>75%) alongside slight perceptible darkening in colour of the leaves. The use of multi-frequency ultrasound in sequential mode is an effective technique for the removal of pesticide residues from leafy vegetables. However, ultrasonic operating conditions should be considered to maintain product quality.