Abstract: he bioaccumulation and biodegradation kinetics of alkyl phenols by Tolypothrix were studied and compared.The growth of microalgae during the 5 d period underwent lag,exponential and stationary growth phases.The average bioaccumulation factor of phenol,o-cresol,m-cresol and 4-octylphenol by Tolypothrix was calculated as 4.59,3.87,5.82 and 292.48 respectively,and had linear correlation with octanol/water partition coefficient(KOW).The average biodegradation rates of phenol,o-cresol,m-cresol and 4-octylphenol were found to be 2.54,3.17,1.84 and 0.16 mg/L respectively. Based on the newly proposed second-order kinetic equation,the second-order constants K of phenol,o-cresol,m-cresol and 4-octylphenol by Tolypothrix were 0.386,0.500,0.254 and (0.023) respectively.Mainly determined by the initial compound concentration,the value of K had the linear correlation with molecular weight(M):K=-0.003M+0.69,R=0.87,N=4.