The pure rotational transition of the NF radical in the second electronically excited state, b (1) Sigma(+), was detected by microwave spectroscopy. The NF radical was generated by de-discharge through a mixture of NF3 and H-2 at around 90 K. Six rotational transitions for upsilon = 0 and four for upsilon = 1 were observed in the 73-442 GHz region. In addition to the rotational and centrifugal distortion constants, the quadrupole coupling constant of the nitrogen nucleus of NF(b (1) Sigma(+)) was determined for the first time from the lowest two transitions of NF in the upsilon = 0 level. The spectrum of NF(alpha (1) Delta) in the first vibrational excited state was also observed in order to derive highly accurate potential parameters for comparison with the data of NF(X (3) Sigma(-), b (1) Sigma(+)).