Abstract: On 28 March 2009, a west to east oriented cold front appeared in the southern part of China around 25°N. With the development of the cold front, convective precipitation echoes were firstly detected in the early afternoon near Wuzhou, Guangxi province, then it moved eastward and organized into an MCS, and brought thunderstorm, heavy rain, and hail to most central and western parts of Guangdong province and the Pearl River Delta in the late afternoon. The analyses of the AWS (Automatic Weather Station) data, the radar echo data, the satellite images, the NCEP-FNL reanalysis data, and the successful simulation results from the mesoscale research model (WRF) are used to examine the development of the convection and its relation to the frontogenesis. The results show that the frontal convection initiated along a mesoscale surface convergence line with almost 200 km in length, and the convective storm was likely triggered in the regions with large CAPE and small CIN values. With the development of the convection, the front intensifies. Frontogenesis calculations showed that both the diabatic process and the tilting terms were important in the lower troposphere frontogenesis, but the effects of the deformation and horizontal convergence processes were small. The diabatic process mainly caused frontogenesis in the ascending branch of a secondary circulation driven by the frontal convection, while the tilting term contributed to frontogenesis mostly in the descending branch, which are different from those frontogenetic processes driven by large scale forcing, and suggest that mesoscale frontogenesis is primarily driven by the thermally direct ageostrophic circulation. Analyses of relative vorticity and vertical motion along the frontal zone found that there was a good correspondence between the 850 hPa positive vorticity maxima and the upward motion at 500 hPa, demonstrating that the CISK (Conditional Instability of the Second Kind) like driving mechanism is responsible for the interaction between the convection and the mesoscale frontogenesis. The convection acted to enhance the frontogenetic process, while the front helped organize the convection into the MCS. As a main cause for this kind of severe weather, that the mesoscale frontogenesis acts to organize convection should be concerned.