The study characterized the biochemical changes associated with long term exposure to pesticides. Practical parameters of pesticides were collected using 500 questionnaires. Farmers having 10 years working period were invited to a private clinic for blood sampling and enzyme analysis. All participants were male farmers of different age groups, and education levels. Occupational parameters indicated that majority of farmers used manual methods for pesticide works. About 130 pesticides are currently used in Gaza. Toxicological symptoms indicated that dizziness, headache, and nausea were dominant among farmers, whereas vomiting abdominal colic and tearing were less dominant. Acetyl Cholinesterase (ACHE) cumulatively inhibited among farmers after work whereas Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST) and Alkaline Phosphatase (ALP) activities were above range after long term exposure. It can be concluded that long term exposure to pesticides may damage liver and kidney cells resulting in hepatic-toxicity and/or nephrotoxicity.