To obtain DNA typing results from forensic biological samples is occasionally difficult, since they are complex and diverse. AmpFℓSTR^® Identifiler^® Plus PCR Amplification Kit (IDPlus) was developed to improve the success rate of DNA typing from such samples by Applied Biosystems. Forensic biologists must be cautious in DNA typing when considering the characteristics of the Kit used for analyzing in such samples. Therefore, to reveal to the characteristics of IDPlus Kit is very important to increase the reliability and probative value of DNA typing in the trial and investigation. In this study, IDPlus is evaluated for the characteristics and the DNA detectability. We also compared IDPlus with AmpFℓSTR^® Identifiler^® PCR Amplification Kit (ID) by analyzing samples difficult to obtain DNA types. The results from the PCR inhibitor study using bloodstain on soil or denim indicated that IDPlus was more resistant to PCR inhibitors than ID. In the study of analyzing degraded DNA, there were no significant differences to be found except for the sensitivity. The peak corresponding to insufficiently amplified products due to a point mutation on primer binding site was higher using IDPlus than ID in electropherogram. Also the anomalous peaks which were observed in analyzing same mammal animal DNA samples were higher. Hence, IDPlus is considered to be very effective leverage to samples analysis which is difficult to detect allele due to PCR inhibitors. The primer binding ability to the template DNA was altered when using IDPlus compared with the ID so this should be taken into consideration. Forensic biologists must be aware the possibility of the discordance of DNA typing results between IDPlus and ID. From the results of this study, IDPlus was considered to be utilized to analyze forensic samples difficult to detect allele using ID.