  This paper concerns the initial-boundary value problem (IBVP) of the Kawahara
equation posed on the right and left half-lines. We prove the local
well-posedness in the low regularity Sobolev space. We introduce the Duhamel
boundary forcing operator, which is introduced by Colliander - Kenig \cite{CK}
in the context of Airy group operators, to construct solutions on the whole
line. We also give the bilinear estimate in $X^{s,b}$ space for $b < \frac12$,
which is almost sharp compared to IVP of Kawahara equation \cite{CLMW2009,
JH2009}.
