A cooling structure of a water-cooled engine includes: a plurality of cylinders 2 arranged in a cylinder block 1; and a water jacket W formed around the plurality of cylinders 2. The water jacket W includes a pair of main flow paths 7, 8 formed in a state of extending in a cylinder arrangement direction outside the cylinders, and inter-bore flow paths 9, 10 formed between adjacent cylinders 2 in a state of connecting the pair of main flow paths 7, 8. Guide walls 11h, 13h, capable of guiding the cooling water flowing in the main flow paths 7, 8 to the inter-bore flow paths 9, 10, are formed in the cylinder block 1.