With desires for safe food, there is growing concern that pesticide spray drift will expose people, plants, and the environment to pesticide residue andpotential negative effects thereof. For highly efficient, safe spray application, technologies for measuring the spray drift should be developed andimproved with some urgency. This study investigated the applicability of two optical particle counters (OPCs), which are mostly used to measureairborne particle mass concentration, for measurement of airborne pesticide spray drift. Experiments were conducted in a controlled laboratory and anash tree orchard to evaluate the handiness and accuracy of two OPCs, OPC 1 and OPC 2. The experimental results indicated that the OPC 1 was betterapplicable to the measurement of spray drift in the field while the use of the OPC 2 was limited due to its narrow range of measurable droplet sizes. The readings of the OPC 1 produced highly accurate results (R2=0.9637) compared to the actual spray drift. For better application of OPCs, this studysuggests the OPCs should be positioned properly to inhale spray droplets of the appropriate size and concentration.