We　investigate　the　time-asymptotic　stability　of　planar　rarefaction　wave　for　the　three-dimensional　Boltzmann　equation,　based　on　the　micro-macro　decomposition　introduced　in　[24,　22]　and　our　new　observations　on　the　underlying　wave　structures　of　the　equation　to　overcome　the　difficulties　due　to　the　wave　propagation　along　the　transverse　directions　and　its　interactions　with　the　planar　rarefaction　wave.　Note　that　this　is　the　first　stability　result　of　planar　rarefaction　wave　for　3D　Boltzmann　equation,　while　the　corresponding　results　for　the　shock　and　contact　discontinuities　are　still　completely　open.