Background: Diabetes mellitus (DM) is a metabolic disorder characterized by hyperglycemia and associated with several risk factors, such as an unhealthy and unbalanced diet. Porang tubers, known as healthy diet resources, contain glucomannan, a substance that has many positive effects, such as ameliorating blood glucose. Porang tubers are processed as many food products, one of which is porang-processed rice (PR). This study investigated the immediate effects of PR on the blood glucose levels compared to white rice (WR) in patients with diabetes mellitus (DM). Methods: This was a pilot study of a non-randomized clinical study with a pre-and post-test design held from July to August 2021 in Diponegoro National Hospital, Semarang, Indonesia, among 40 DM patients. Subjects who met the inclusion criteria were divided into two groups: subjects that consumed Porang-processed rice (PR group, n=20) for two days and those that consumed white rice (WR group, n=20). They were measured for fasting blood glucose (FBG) and 2 hours post-prandial glucose (2hPPG) at baseline (T0) and at day-3 after observation (T1). Data were analyzed using SPSS version 20 for Windows. Results: There were no significant differences in FBG and 2hPPG between the PR group and WR group at T0 and T1 (p>0.05). However, there were slightly larger decreases in FBG and 2hPPG in the PR group compared to the WR group, although they were insignificant (p>0.05). Conclusion: The immediate consumption of PR for only two days in patients with DM could not reduce FPG and 2hPPG. It is needed to be confirmed by further studies whether PR may have the role as adjunctive in inhibiting the dramatic rise of FBG or 2hPPG or stabilizing blood glucose in patients with DM in a more extended time of consumption.