Flexirubin has a broad range of pharmacological effects such as antimicrobial and anticancer activities. The aim of this study was to investigate the adverse effect of flexirubin (Chryseobacterium artocarpi CECT 8497) by acute, sub-acute (28 days repeated dose) oral toxicity and mutagenicity studies. The acute and sub-acute oral toxicity studies were performed in Sprague-Dawley rats (n - 12; male - 6; female - 6/group) as per OECD 425 (up and down procedure) and OECD 407 guidelines respectively. There was no mortality and signs of toxicity in acute and sub-acute toxicity studies. No test substance related differences were observed in body weight, food consumption, clinical signs, organ weight, haematology and serum biochemical parameters in treated groups of flexirubin at a target concentration of 1250, 2500 and 5000 mg/kg body weight per day for 28 days. The no-observed-adverse-effect level (NOAEL) of flexirubin was 5000 mg/kg body weight/day, the highest dose investigated. No evidence of mutagenicity was found, either in vitro (bacterial reverse mutation assay) or in vivo in mice (bone marrow micronucleus assay and sperm shape abnormality assay). The findings of this acute, sub-acute toxicity and mutagenicity studies support the safety of flexirubin extract. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.