Large,　high　optical　quality　single　crystals　of　ruby　have　been　grown　successfully　by　the　floating　zone　method　under　air　atmosphere.　The　size　of　the　grown　crystal　is　typically　60-70　mm　in　length　and　7-8　mm　in　diameter.　The　obtained　crystals　were　red　and　did　not　have　any　macroscopic　defects　such　as　cracks　and　inclusions.　Grown　crystals　were　characterized　by　powder　X-ray　diffraction　(XRD)　methods,　polarized　optical　microscopy,　scanning　electron　microscopy　(SEM).　The　absorption　and　fluorescence　spectra　were　measured　at　room　temperature　and　the　dielectric　constant　measurements　of　ruby　crystals　were　also　presented.　Defects　occurring　in　single　crystals　of　ruby　during　crystal　growth　by　floating　zone　method　are　described,　and　their　correlation　with　the　growth　parameters　is　discussed.　The　origin　and　control　of　these　defects　in　grown　crystals　were　studied　and　the　optimum　method　was　proposed.　(C)　2011　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim