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Maize (Zea mays L.) is one of the most prominent cereal crops playing a crucial role in sustaining global food security. In breeding programs, grain size characters including kernel length (KL), kernel width and kernel thickness are importantly considered for the evaluation of kernel weight. The KL was reported to be significantly and positively correlated with the kernel size or/and kernel weight, as well as the final grain yield of maize. In the present study, the haploid lines derived from the intermated B73×Mo17 Syn 10 doubled haploid (IBM Syn10) mapping population were used to identify the putative QTLs for KL in different agro-ecological environments and to understand the stability of QTL across environment. The linkage map, consists of 6540 markers, with an average chromosome length of 1113.6 came were used for QTL mapping. The major findings of the present experiment are summarized below.1. Phenotypic data revealed that maize KL varied significantly under the main effect as well as the interaction of different environments and DH lines. Under all the environments, the average KL of DH lines was quantitatively higher than their parents, suggesting the efficacy of intermating for ten generations. Higher broad sense heritability (0.89) and lower kurtosis as well as scenes values (<1.0) of KL under different environments indicated the significance of genetic factors in the formation of KL, and suggested that KL could be effectively increased by selective breeding programs.2. The QTL analysis of IBM Syn10 DH lines revealed thirty six putative QTLs (LOD>2.5) associated with KL, among these 12 and 24 QTLs were specifically identified in Heilongjiang and Yunnan environments, respectively. All the identified QTLs were well distributed over all the 10 maize chromosomes. Seven putative QTLs were found on chromosome 1 and 8, six QTLs on chromosome 2, and three QTLs for each on chromosome 6, 9 and 10. Only one QTL was observed on chromosome 4 as well as chromosome 5, while two QTLs were observed on chromosome 3.3. All the observed putative QTLs were environment specific, i.e. present only in a single environment. The LOD scores ranged from 2.51 to 7.36, while the observed phenotypic variance was in the range of 2.80 to 8.94％. Out of 36, only 18 QTLs individual accounted for more than 5% of phenotypic variation. The parent with large KL (Mo17) contributed to increasing effects for 21 QTLs (58%), with 12 QTLs with >5% phenotypic variations, indicating that the Mo17 is a good donor for improving maize KL. Whereas, the small-KL parent B73 contributed to the other 15 QTLs (42%), embracing the only 6 QTL explaining>5% of phenotypic variation. Two QTLs (qKL1-3 and qKL8-4) were present twice in a particular environment, although these QTLs have smaller effects. At chromosome 1, two other QTLs, qKL1-1 and qKL1-2 explained higher phenotypic variance (7-9%) and LOD (5.7-7.4). The QTLs at chromosome 3 (qKL3-2), chromosome 8 (qKL8-2), chromosome 9 (qKL9-3) also showed around 8%of phenotypic variations.