Honeycombs　are　widely　used　in　aerospace　structures　due　to　their　low　density　and　high　specific　strength.　In　this　paper,　effective　electromagnetic　properties　of　irregular　honeycombs　are　investigated,　by　using　the　three　dimensional　homogenization　theory　and　corresponding　computational　procedure.　This　homogenization　method,　being　the　extension　of　two-scale　asymptotic　approach,　is　employed　to　determine　the　expressions　of　the　effective　dielectric　permittivity,　magnetic　permeability　and　electrical　conductivity.　To　verify　and　validate　the　proposed　model　and　procedure,　effective　permittivities　of　a　typical　irregular　honeycomb　are　studied　and　compared　with　those　of　semi-empirical　formulae.　Moreover,　the　effect　of　geometry　of　honeycomb＇s　unit　cell　on　effective　permittivities　is　also　examined.　Compared　to　semi-empirical　estimations,　the　two-scale　asymptotic　homogenization　method　can　be　used　to　achieve　more　accurate　results　of　effective　electromagnetic　properties　for　honeycombs　in　the　scope　of　numerical　modeling,　and　it　can　be　also　extended　for　estimation　of　effective　electromagnetic　tensors　for　various　periodic　composites.　Copyright　©　2014　Tech　Science　Press.