  We discuss c\bar{c} and b\bar{b} pair productions at ep collider for studying
extremely small x(g) region. It has been shown that Large Hadron electron
Collider (LHeC) has a reach of about x(g)>10^{-6}. The aim of this work is to
show that the PDF uncertainties in the heavy flavour production. Maximum
difference of cross section between PDFs 60% has been found in the process of
ep\rightarrow eq\bar{q}X.
