Field experiments were conducted to determine whether varietal differences in protein content exist and to study the use of cultural practices — plant density, time of N application, and application of chemicals —for increasing protein content of rices (Oryza sativa L.). Results demonstrated that a high‐yielding improved line ‘IR480‐5‐9’ has high protein content in the grain. The protein content of brown rice of IR480‐5‐9 varied from 9.5 to 10.2% without application of N. The highest protein of ‘IR480,’ was about 12.5% while that of ‘IR8’ was 9.8%. In another experiment, the protein content of IR480 was 10.2%, while that of ‘IR22’ was 8.6%. Both rices had similar grain yields (7.8 metric tons/ha). In another experiment, the protein content of several rice cultivars was significantly higher when 150 kg/ha N was applied half at planting and half at heading than when all N was applied at planting. Simetryne [2,4‐bis (ethyl amino)‐6‐(methyl thio)‐S‐triazine], at 0.5 kg/ha active ingredient, applied either as granular or liquid formulation at panicle initiation or at heading stage of the rice crop, significantly increased the protein content and protein yield of IR22 compared with the fertilized control. Three chemicals, tenoran [N′‐4 (4‐chlorophenoxy) phenyl‐N,N‐dimethyl urea], CP 17029 [2,4 bis (3 methoxy‐propyl amino)‐6‐(methyl thio)‐Striazine], and benzomarc (N‐benzoyl‐N‐dichloro‐3,4‐phenyl N′‐N′‐dimethyl urea) also increased protein content of rice grain without significantly affecting grain yields and yield components.

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