An intervention to reduce insecticide exposure in Shogun orange farmers was implemented in Krabi Province, Thailand. Intervention effects on insecticide-related knowledge and attitude were evaluated in a quasi-experimental study in two farms about 20 kilometers (km) apart. The intervention was conducted at one farm; the other served as control. The study included 42 and 50 farmers at the intervention and control farms, respectively. The intervention included several components, including didactic instruction, practical demonstrations, use of a fluorescent tracer, and continuing guidance on insecticide use via a small, specially trained group within the overall intervention group. To the best of our knowledge, this was the first such intervention in Thailand. Knowledge and attitude were measured at baseline (pre-intervention), and at 2 and 5 months after the intervention (follow-up 1 and follow-up 2, respectively). Intervention effects were assessed with linear mixed models, specified to enable testing of effects at each follow-up time. The intervention was associated with substantial and statistically significant improvements in both knowledge score and attitude score (P < 0.001 for each score at each follow-up time). Intervention-related improvements in knowledge score and attitude score were equivalent to about 27% and 14% of baseline mean knowledge and attitude scores, respectively. Intervention-related benefits were similar at both follow-up times. Findings were similar before and after adjustment for covariates. These findings increase confidence that well-designed interventions can reduce farmers’ insecticide exposure in Thailand and elsewhere. In future research, it would be desirable to address long-term intervention effects on farmers’ health and quality of life.