Cattle internal organs as accessible raw materials have a long history of being widely used in beef processing, feed and pharmaceutical industry. These traits not only are of economic interest to breeders, but they are intrinsically linked to many valuable traits, such as growth, health, and productivity. Using the Illumina Bovine HD 770K SNP array, we performed a genome-wide association study for heart weight (HW), liver weight (LIW), spleen weight (SW), lung weight (LUW) and kidney weight (KW) in 1217 Simmental cattle. In our research, 38 significant single-nucleotide polymorphisms (SNPs) (p<1.49×10-6) were identified for 5 internal organ weight traits. These SNPs are within or near 13 genes and some of them have been reported previously, including NDUFAF4, LCORL, BT.94996, SLIT2, FAM184B, LAP3, BBS12, MECOM, CD300LF, HSD17B3, TLR4, MXI1 and MB21D2. In addition, we detected four haplotype blocks on BTA6 containing 18 significant SNPs associated with SW. Our results offer worthy insights into understanding the genetic mechanisms of internal organs' development, with potential application in breeding programs of Simmental beef cattle.