We derive astrophysical and structural parameters of open clusters NGC 1245 and NGC 2099 from 2MASS JHKs and Gaia DR2 photometric / astrometric data bases. Their likely members have been determined from Gaia DR2 proper motion data. Our E(B – V) values (2MASS) are slightly smaller than the literature values, whereas our E(B – V) values (Gaia DR2) agree with the literature within the uncertainties. Their distance moduli/distances and ages are in good coincident with the literature. NGC 1245 has steep negative core mass function slope (MFs) (χ_core=-1.24). It’s at halo (χ_halo=+0.78) and at overall (χ_overall=-0.95) MFs mean that it presents signs of small-scale mass segregation to the outer regions from its core, due to its [t_rlx (overall),τ_overall ]=[302 Myr,5]. The MFs of NGC 2099 is very negative steep (χ_core=-2.67) in the core, and quite positive steep (χ_halo=+1.41) in the halo. This kind of MF slope steeping from the core to the outskirts indicates that low-mass stars in the core are transferred to the cluster's outskirts, while massive stars sink in the core, because of mass segregation. NGC 2099's flat overall MFs (χ_overall=+0.91) and its τ_overall=8 presents a sign of mass segregation. These OCs with the relatively large masses 8700 Msolar (NGC 1245) and 5660 Msolar (NGC 2099), which locate at RGC > 9 kpc, expose to external perturbations such as tidal effects and shock waves, and they lose their stars in low-proportions.