Hoshaiah Rabbah or Hoshaʻyā Rabbā (Hebrew: הושעיה רבה) was an amora of the first generation in Rabbinic Judaism and a compiler of baraitot explaining the Mishnah and the Tosefta.
Johanan bar Nappaha, one of his greatest disciples, declared that Hoshaiah in his generation was like Rabbi Meir in his: even his colleagues could not always grasp the profundity of his arguments according to Eruvin 53a.
According to Peah 8:21b, Hoshaiah's consideration for others is exemplified in his gracious apology to the blind teacher whom he had engaged for his son and whom he did not suffer to meet visitors at dinner for fear that he might be embarrassed.
Hoshaiah's authority must have been very powerful in his later years, when he successfully resisted the efforts of Gamaliel III, the son of Judah ha-Nasi, to introduce demai into Syria according to the Jerusalem Talmud, Ḥallah 4:60a.
It is also indicated by his remarkable interposition regarding the Mishnah, which declares that "a Gentile's testimony in the case of an agunah is allowed only if stated as a matter of fact and without any intention to testify" in Yebamot 16:5; and 121b.
Hoshaiah was called the "father of the Mishnah," not so much because of his collection and edition of the mishnayot as because of his ability to explain and interpret them according to Kiddushin 1:60a and Bava Kamma 4:4c.
His most important halakhic decision is directed against the standard weights and measures, held by Johanan bar Nappaha to be traditional from the Sinaitic period.
Bacher quotes a passage in which Hoshaiah refuted the incarnation dogma: So, when the Holy One blessed be He created Adam the first man, the ministering angels erred concerning him and sought to proclaim 'holy' before him.
Hoshaiah was very strict in requiring from a proselyte both circumcision and mikveh immersion in the presence of three rabbis according to Yevamot 46b; this was very likely directed against the free conversion of gentiles by Judaizing Christians.