MK spectral classifications are given for 591 stars which are used for time and latitude observations at Mizusawa and Washington. The classifications in the MK system were made by slit spectrograms of dispersion 73 A/mm at H-gamma which were taken with the 91cm reflector at the Okayama Astrophysical Observatory. Photometric observations in UBV were made with the 1-meter reflector at the Flagstaff Station of U.S. Naval Observatory.