With rice cultivars Yangdao 6 (Indica) and Wuyujing 3 (Japonica) as test materials, the effects of relatively high temperature (RHT, mean temperature 30 degrees C) at grain-filling stage (GFS) on the starch viscosity profile and magnesium (Mg) and potassium (K) contents of rice grain were studied in a phytotron. Four temperature treatments were installed, i.e., RHT at whole GFS, RHT at early GFS and optimum temperature at later GFS, optimum temperature at early GFS and RHT at later GFS, and optimum temperature (CK, mean temperature 23 degrees C) at whole GFS. The results showed that RHT at GFS significantly influenced the characteristic values of rice grain' s starch viscosity profile, e.g., the values of gelatinization temperature, final viscosity, consistency, and setback increased, while those of peak viscosity, hot viscosity, and breakdown decreased, with Yangdao 6 and Wuyujing 3 followed the similar pattern. The RHT increased the contents of Mg, K, and N, especially of K, resulting in a marked decrease of Mg/K and Mg/(N * AC * K) in the grain. The grain's amylase content (AC) of the two cultivars showed contrasting in response to temperature treatments. Wuyujing 3 performed decrease, while Yangdao 6 exhibited increase in AC values. The RHT at whole GFS affected the starch viscosity profile and the Mg and K contents most greatly, followed by the RHT at early GFS, and the RHT at later GFS. The period within 20 days after flowering was the key period during which temperature affected the grain's starch viscosity profile and Mg and K contents. The Mg/K and Mg/ (N * AC * K) in rice grain significant correlated with the characteristic values of starch viscosity profile, which could be used as the reference indices of rice eating quality.