The growth defects in BiB3O6 (BIBO) crystals have been investigated by white-beam synchrotron radiation topography for the first time. It is found that inclusions, dislocations and growth sector boundaries are the primary growth defects nearby the seed. The area away from the seed is nearly free of defects. Based on the experimental observations, the formation mechanism of brown region in BIBO crystals is discussed. Twins and growth sector boundarie exist in the brown region, which is the key reason resulting in brown presentation. The approaches to reduce and eliminate the defects are presented. (C) 2002 Elsevier Science B.V. All rights reserved.