The inhibition of human salivary α-amylase activity in forensic samples can lead to false negatives in α-amylase activity-based saliva screening tests. This study aimed to develop and validate an α-amylase inhibition-resistant saliva presumptive test using the Ohta and Ohmura’s modified blue starch agarose plate (OhM) method, incorporating bovine serum albumin and calcium chloride. To assess the effectiveness of the OhM method, we compared its positive detection rate to that of the conventional method through various validation experiments. In a mixture experiment using commercial beverages, the OhM method successfully detected positive reactions in samples that tested negative using the conventional method. Our results demonstrate that the OhM method is a practical and sufficient technique for identifying saliva in forensic samples that may be subject to α-amylase inhibition.