Various magnetic properties of one dimensional antiferromagnet Cu(C6H5COO)2·3H2O were investigated by means of magnetic susceptibility, magnetic torque, NMR, and ESR measurements. The results show that this compound is one of the best one dimensional antiferromagnets known at present. An intrachain exchange interaction J/K was estimated to be -8.6 ± 1°K while no second order phase change was found down to 1.4°K. ESR line width at room temperature was not explained by an usual treatment and an anisotropic exchange effect was newly taken into account. However, other anomalies of the line width such as the frequency, temperature, and angular dependences appeared at low temperature regions were not yet explained.