The potential use of simultaneous thermal technology has been explored for quantifying mixed calcium oxalate monohydrate and dihydrate, which are major mineral components of urinary stones. Based on the observation and theoretical analysis of thermal dehydration of calcium oxalates, an effective and simple method has been developed for quantitative analysis of calcium oxalate hydrates. The present approach would be useful in medical practice and in quantifying inorganic hydrates with water-containing crystals similar to calcium oxalate hydrates.