Abstract: Purple heading Chinese cabbage inbred line‘14S838’and common Chinese cabbage inbred line‘15S1080’were used as male parent and female parent，respectively，and F1 and F2 populations were constructed to study the genetic law of purple heading trait in Chinese cabbage. The results showed that the inner leaves of leaf-head were purple in F1 population，but the purple area was smaller than that of its purple parent‘14S838’. The segregation ratio of purple heading individuals to non-purple individuals fitted to the ratio of 3︰1 in F2 population，which indicates that purple heading of Chinese cabbage was a quality trait and consistent with genetic pattern of a single dominant gene. Purple height ratio（purple height/leaf head height），purple width ratio（purple width/leaf head width）and purple area ratio（purple area/leaf head area）were used to describe purple size trait in purple single plant of the F2 generation，and results indicate that the broad-sense heritability of these three parameters was 94.00%，87.72% and 83.33%， respectively. The result meant that the variation of purple size was mainly controlled by genetic factors，while the external environment showed little influence. The frequency distribution histograms showed that the purple height ratio and the purple width ratio were accorded with normal distribution but the purple area ratio showed positively skew distribution，which indicated that the purple size trait was a quantitative character. Further analysis found the high correlation existed between purple height ratio，purple width ratio and purple area ratio. According to the measurement operation，the purple area ratio was accurate but more complicated to measure. However，measurement of the purple height ratio was simple. Moreover，the purple height ratio was accompanied with high hereditary capacity and highly correlated with the purple area ratio. Hence，the purple height ratio can be used instead of the purple area ratio to define the purple size of the purple heading Chinese cabbage.

Key words: Chinese cabbage, purple heading, quality-quantitative trait, genetic analysis