Abstract: Microcapsules of pendimethalin with a urea-formaldehyde resin wall were prepared by an in-situ condensation polymerization reaction in aqueous medium. Several encapsulating parameters including dispersing and emulsifying agent,emulsification time,stirring speed,acidification time and curing temperature on microcapsule appearance quality such as encapsulation rate,particle size,and size distribution were investigated. Optimal reaction conditions were as follows:PAAS and SMA at weight ratio of 4 ∶ 1,stirring for emulsifying at speed of 1 500 r/min and lasted 60 min,acidifying for 90 min,the curing temperature under 50℃ for 90 min. Under these conditions,the mean particle diameter of 10 μm,uniform and spherical microencapsules of pendimethalin were obtained,their encapsulation rate was above 99%.