A series of novel monohalovinylated pyrethroids are designed and synthesized to replace one halo atom with a hydrogen atom on the double bond of dihalopyrethroids. Bioassays indicate that some of the synthesized compounds, such as 3j and 1j, exhibit high insecticidal activities against mosquitoes ( Culex pipiens pallens ), oriental armyworms ( Mythimna separata ), alfalfa aphids ( Aphis medicagini ), and carmine spider mites ( Tetranychus cinnabarinus ). Photolytic results of E-cis-1j suggest that monohalovinylated pyrethroids are photodegraded more easily than compound 12.