ω-Chloromethyl longifolene (Ic) was synthesized via halogenation of ω-hydroxymethyl longifolene (Ib) with thionyl chloride as halogenating reagent and structurally characterized by means of FTIR, 1HNMR，13CNMR and HRMS (ESI). There were obvious effects of reaction temperature, reaction time and material ratio on the halogenations reaction. Under the optimum reaction conditions (85°C, 6h, molar ratio for thionyl chloride: compound Ib=1.10:1.00), the yield of compound Ic was up to 94.2%. The preliminary biological activity test showed that Ic could obviously inhibit the growth of two bacteria (staphylococcus aureus and Canidia Albicans) and one fungus (Klebsiella pneumonia) with MIC 31.25, 62.5, and 125mg/L, respectively, comparing with 500mg/L of MIC of longifolene. It was found that Ic exhibited obviously higher antimicrobial activity, which was associated with its lower HOMO (highest occupied molecular orbital)/LUMO (lowest unoccupied molecular orbital) energy gap (0.063 a.u), comparing with that of longifolene (0.256 a.u) calculated using the density function theory (DFT) at B3LYP/6-31G level.