The pure rotational spectrum of YbOH has been recorded and analyzed to produce fine and magnetic hyperfine parameters for the (X) over tilde (2)Sigma(+)(0, 0, 0) state. These parameters are compared with those determined from the optical study (Melville and Coxon, 2001) and with the values for YbF (Dickinson et al., 2001). The results support the existence of an unobserved perturbing state near the (A) over tilde (2)Pi(1/2) state, similar to that previously found in YbF. The precisely determining parameters lays the foundation for laser cooling YbOH, which will aid in the search for new physics beyond the standard model.