  We present K-band observations of five Mira stars with the IOTA
interferometer. The interferograms were obtained with the FLUOR fiber optics
beam combiner which provides high-accuracy visibility measurements in spite of
time-variable atmospheric conditions. For the Mira stars X Oph, R Aql, RU Her,
R Ser, and V CrB we derived the uniform-disk diameters 11.7 mas, 10.9 mas, 8.4
mas, 8.1 mas, and 7.9 mas (+/-0.3 mas), respectively. Simultaneous photometric
observations yielded the bolometric fluxes. The derived angular Rosseland radii
and the bolometric fluxes allowed the determination of effective temperatures.
For instance, the effective temperature of R Aql was determined to be 3072 K
+/- 161 K. A Rosseland radius for R Aql of 250 Rsun +/- 63 Rsun was derived
from the angular Rosseland radius of 5.5 mas +/- 0.2 mas and the HIPPARCOS
parallax of 4.73 mas +/- 1.19 mas. The observations were compared with
theoretical Mira star models of Bessel, Scholz and Wood (1996) and Hofmann,
Scholz and Wood (1998).
