98.7% for the response. The obtained maximum MC-LR removal efficiency was 98% under the optimum conditions. The prepared nanocomposite was approved as a promising nano-photocatalyst for MC-LR removal under visible-light irradiation. The BiVO4/TiO2 as an important nano-catalyst with technological potential can be used directly in environmental preservation, specifically in the decontamination of MC-LR from aqueous solutions. Keywords: Microcystin-LR (MC-LR), BiVO4/TiO2, Nanocomposite, Hydrothermal, Photocatalysis, Visible light Introduction Cyanobacteria are a group of microalgae that are known as the oldest oxygen-producing organisms (3.5 billion years) and called blue-green algae, Myxophyceae, Cyanophyceae and Cyanophyta [1,2]. Many cyanobacteria produce a wide variety of toxins (cyanotoxins) include Hepatotoxins, neurotoxins, cytotoxins, dermatoxins and irritant toxins [3]. Among them, Hepatotoxins are the most prevalent cyanobacterial toxins [4,5] that are included microcystins, nodularins, and cylindrospermopsins [1]. Microcystins (MCs) are potent hepatotoxins produced by the number of planktonic cyanobacteria such as Anabaena, Anabaenopsis, Oscillatoria, Nostoc, Planktothrix, and Microcystis [6]. These toxins are very soluble in water and based on their two variable amino acids have more than 80 variants [7,8]. The US Environmental Protection Agency (US-EPA) has a special concern to 4 MCs (LR, RR, YR, and LA). The main structural difference between these is the replacement of single amino acids [9]. Microcystin-leucine-arginine (MC-LR) is one of the most studied cyanotoxins due to its toxicity and abundant [10]. Moreover, the World Health Organization (WHO) is recommended a limit of 1 μg/L for total MC-LR for water for human consumptions [11]. MCs cause poisoning for livestock and wildlife and also pose a health hazard for humans through of the drinking water [12]. When MCs ingest orally absorb to hepatocytes and prohibit protein phosphatase, subsequently resulted in cell structures disruption, intrahepatic hemorrhage, and death [13]. In 1996 MC-LR was responsible for the death of least fifty Brazilian kidney dialysis patients [14]. Also, Huisman et al. reported the episodes including skin and respiratory irritations,gastrointestinal disease among swimmers on the Queensland coast from 1996-1998, and a further prevalence of illness among hemodialysis patients in 2001 [15]. Various techniques have suggested for the cyanobacteria cells and MCs control in drinking water, such as coagulation, flocculation, filtration, activated carbon, nanofiltration, oxidation processes and etc. [16,17]. Recently, in order to remove these toxins in raw waters, more studies have focused on the application of advanced oxidation processes using (AOPs) such as UV/H2O2 [18], Fenton regents [19-20], and>