Exposure to organophosphates (OP) is an occupational hazard among farmers in low income countries. In Kenya most farmers lack adequate personal protective equipment (PPE), have low level of awareness and inadequate knowledge on organophosphate toxicity. The objective of this study was to determine factors associated with Serum Cholinesterase levels among farmers in Keiyo North Sub-County. A cross sectional study was conducted during the month of June to August 2013. Multi Stage sampling methodology based on probability proportional to size (PPS) was used to select the study sites. Systematic sampling was used to select households. Data was collected using a pre-tested questionnaire and blood sample obtained from farmers to determine serum cholinesterase levels. Bivariate and multivariate analyses were conducted to determine factors associated with abnormal serum cholinesterase. The prevalence of abnormal serum cholinesterase levels among the 390 enrolled farmers was 13% .The most common related symptoms as experienced by the farmers with depressed SChE(Serum Cholinesterase Enzyme) after spraying were headache (84.4%), dizziness(76.2%) weakness (66.9%) and burning sensation on the skin (64.9 %). Farmers of the age group 26- 35 years (OR=0.6; 95% CI: 1.24-7.79), handling Dimethoate OP (aOR=9.7; 95% CI: 1.83-25.83), permanent farm workers (aOR=5.5; 95 % CI: 2.32-8.51) and unrecommended practices when spraying, (aOR=1.9; 95% CI: 1.34-11.33) were significantly associated with OP toxicity. In conclusion the major exposure factors were Dimethoate use and being a permanent farm worker. Analysis of factors associated with abnormal cholinesterase can form a basis for policies and regulations aimed at promoting safer farm practices for farmers. The two ministries of health and agriculture should integrate health education and trainings on recommended farm practices.