Context : PKS 1749+096 is a BL Lac object showing weak extended jet emission to the northeast of the compact VLBI core on parsec scales .

Aims : We aim at better understanding the jet kinematics and variability of this source and finding clues that may applicable to other BL Lac objects .

Methods : The jet was studied with multi-epoch multi-frequency high-resolution VLBI observations .

Results : The jet is characterized by a one-sided curved morphology at all epochs and all frequencies .
The VLBI core , located at the southern end of the jet , was identified based on its spectral properties .
The equipartition magnetic field of the core was investigated , through which we derived a Doppler factor of 5 , largely consistent with that derived from kinematics ( component C5 ) .
The study of the detailed jet kinematics at 22 and 15 GHz , spanning a period of more than10 years , indicates the possible existence of a bimodal distribution of the jet apparent speed .
Ballistic and non-ballistic components are found to coexist in the jet .
Superluminal motions in the range of 5–21 c were measured in 11 distinct components .
We estimated the physical jet parameters with the minimum Lorentz factor of 10.2 and Doppler factors in the range of 10.2–20.4 ( component C5 ) .
The coincidence in time of the component ’ s ejection and flares supports the idea that , at least in PKS 1749+096 , ejection of new jet components is connected with major outbursts in flux density .
For the best-traced component ( C5 ) we found that the flux density decays rapidly as it travels downstream the jet , accompanied by a steepening of its spectra , which argues in favor of a contribution of inverse Compton cooling .
These properties make PKS 1749+096 a suitable target for an intensive monitoring to decipher the variability phenomenon of BL Lac objects .

Conclusions :