Abstract: A 15% lambda-cyhalothrin microcapsule suspension of polyurea resin was prepared as a capsule material by interfacial polymerization. In the preparation of lambda-cyhalothrin microcapsule suspension, the initial oil-water ratio (R_i) was obtained by the quotient of the weight of the oil phase and the weight of the initial water. The effect of the R_i value on the physico-chemical properties of the lambda-cyhalothrin microcapsule suspension was also investigated. Four 15% lambda-cyhalothrin microcapsule suspensions treated with different initial oil-water ratios were prepared. Their R_i values were 1 : 0.55, 1 : 0.69, 1 : 0.83 and 1 : 0.97, respectively. The morphology of the microcapsules was characterized by optical microscope (OM), scanning electron microscope (SEM) and laser particle size analyzer. The encapsulation efficiency and storage stability of each treatment were determined. The experimental results showed that, when the R_i values were 1 : 0.83 and 1 : 0.97, the 15% lambda-cyhalothrin microcapsule suspension had high capsule quality, good microcapsule morphology, and the microcapsule encapsulation efficiency was 90% or higher. The particle sizes were in the range of 3-4 μm (D₉₅), and the storage stability has also be qualified. This study has provided a reference for the preparation of lambda-cyhalothrin microcapsule suspensions.