This study was to examine the effects of certain methodologic choices for testing glycemic index (GI), incremental area under curve (IAUC), and blood glucose responses in 12 healthy adults, who were fed white rice, rice porridge, and overnight rice. Blood samples were collected from venous plasma (VP), capillary plasma (CP), and capillary blood (CB). The results showed the mean GI value (VP; 87 ± 2.5, CP; 85 ± 2.5, and CB; 84 ± 2.6); the mean IAUC (CB; 5006 ± 292, CP; 4844 ± 287, VP; 3784 ± 221 ); the mean postprandial glucose response (CB; 118.2 ± 3.3, CP; 115.2 ± 3.2, VP; 90.7 ± 2.4); Significant correlation was observed between three sampling methods (p < 0.01). In conclusion, the VP sampling approach had a lower degree of dispersion and a higher stability that is a more effective methods to determine GI, IAUC and blood glucose responses. and rice porridge produced the highest GI, followed by white rice and overnight rice.