  We study the O-type star HD 161853, which has been noted as a probable
double-lined spectroscopic binary system. We secured high-resolution spectra of
HD 161853 during the past nine years. We separated the two components in the
system and measured their respective radial velocities for the first time. We
confirm that HD 161853 is an $\sim$1 Ma old binary system consisting of an O8 V
star ($M_{\rm A,RV} \geq 22$ M$_\odot$) and a B1--3 V star ($M_{\rm B,RV} \geq
7.2$ M$_\odot$) at about 1.3 kpc. From the radial velocity curve, we measure an
orbital period $P$ = 2.66765$\pm$0.00001 d and an eccentricity $e$ =
0.121$\pm$0.007. Its $V$-band light curve is constant within 0.014 mag and does
not display eclipses, from which we impose a maximum orbital inclination $i=54$
deg. HD 161853 is probably associated with an H II region and a poorly
investigated very young open cluster. In addition, we detect a compact emission
region at 50 arcsec to HD 161853 in 22$\mu$m-WISE and 24$\mu$m-Spitzer images,
which may be identified as a dust wave piled up by the radiation pressure of
the massive binary system.
