Who was the author of the Mahaprajnaparamitasastra大智度論(T1509)? Traditionally it was believed to be Nagarjuna龍樹, and scholars until fairly recently thought that Kumarajiva鳩摩羅什only modified the text. Currently, however, the opinion that Kumarajiva was himself the author is gaining ground. This opinion is based on circumstantial evidence, though, and is not supported by any textusl evidence. In this paper, I would like to go back to the original view and argue that Nagarjuna was in fact the author, based on textual evidence. There are a number of original ideas in the Sastra, but of these, Pratyutpannabuddhasammukhavasthiasamadhi般舟三眛(Buddhanusmrtisamadhi念仏三眛), in particular, deserves careful attention. The author of the Sastra defined this Pratyutpannasamadhi as "Upaya." Usually Upaya (i.e., Upaya-kausalya善巧方便) refers to the means for Sattva-paripacana教化衆生. On the other hand, "Upaya" (i.e., Pratyutpannasamadhi in the Sastra) is the presupposition of Upayakausalya, "Pre-upaya"前方便, as it were. This definition in the Sastra matches the description in the Bodhisambharasastra菩提資糧論(T1660), which has been proven to be of Nagarjuna's authorship. However, this definition cannot be found in books of Kumarajiva (i.e., the Tchou wei mo kie king注維摩詰経(T1775) and the Kieou mo lo che fa che to yi大乗大義章(T1856)). In addition, the author of the Sastra regarded Prajnaparamita般若波羅密fa che as more important than Upaya, whereas Kumarajiva in the Tchou wei mo kie king regarded Upaya as more important than Prajnaparamita. In conclusion, I maintain that Nagarjuna was the author of Sastra and that Kumarajiva only made modifications.