Abstract:Proline (Pro) content and heat tolerance were determined in a hydroxyproline-resistant line Hypr01 selected in vitro from seedlings of Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee. Hypr01 had higher content of free Pro than the original cultivar Liushitianteqing. A greater increase of free Pro content could be found in Hypr01 under heat stress at 35℃, which was 4 times as much as that in Liushitianteqing and nearly 2 times in heat tolerant cultivar Sijiu. Compared to the control, the callus induced from Hypr01 shoots showed vigorous，root differentiation ability and high fresh weight increment when cultured under successive stress at 35℃． Under such condition，the relative electrolyte leakage，callus browning rate and the content of MDA in Hypr01 were significant lower，but the activities of SOD and CAT in Hypr01 was higher．The plantlets regenerated from Hpyr01 grew better than those from Liushitianteqing under a heat stress condition(35℃ by day and 25℃ by night both for 12 h) in phytotron，and had lower electrolyte leakage and higher fresh weight increment，which indicated a greater heat tolerance.