The number of vascular bundles in the stem is a key factor that affects the nutrient transport and the lodging resistance in maize. Here we deployed an association panel including 172 maize inbred lines to analyze the difference between the number of small vascular bundles (NSVB) and the number of large vascular bundles (NLVB) in the uppermost internode of maize stem, followed by the multiple comparison analysis to learn about the difference and the trend in the number of vascular bundles among different heterosis groups. The results showed that coefficients of variation of NSVB and NLVB in the uppermost internode in different inbred lines were 17.47%~21.69% and 25.83%~32.19%, respectively. The highly significant differences on either of NSVB and NLVB were revealed in different inbred lines. The broad-sense heritability on NSVB and NLVB was 78.87% and 82.58% respectively, while a significantly positive correlation on NSVB in relative to NLVB was observed. Both NSVB and NLVB represented a similarity on the tendency in different heterotic groups (Lancaster < Reid < P < LRC < TSPT). Collectively, this study represented a preliminary understanding of the genetic variation in the number of vascular bundles in different maize inbred lines, and laid a foundation for future quantitative trail locus (QTL) mapping and gene cloning.