The second tithe (Hebrew: ma'aser sheni מעשר שני) is a tithe mentioned in the Hebrew Bible and practised within Orthodox Judaism. It is distinguished from the first tithe (Hebrew: ma'aser rishon מעשר ראשון), the third or poor tithe, and the terumat hamaaser.

In the days of the Temple in Jerusalem, the second tithe involved the setting aside of one tenth of specific agricultural produce during the first, second, fourth and fifth years of each seven-year cycle, for the purpose of taking it to the holy city of Jerusalem, and consuming it there.

Instructions for the second tithe are provided in Deuteronomy 14:22–27, supported by references in Deuteronomy 12:11–18 and 26:12. Deuteronomy 14:28–29 provides instructions for the third or poor tithe, which is performed in the third and sixth years of the seven-year cycle. The remaining seventh year is described as the Shmita, the Sabbatical Year.

As described, the tithe should be of grain, wine, and olive oil, but if the distance to Jerusalem made the carriage of these crops unreasonable, the monetary value of the tithe could be brought to Jerusalem instead, and used to purchase anything edible that the owner desired to eat there - an ox, a sheep, some wine, or beer, or "whatever your soul desires" - for a feast with the person's household in the presence of God.

The Mishnah, in Tractate Rosh Hashanah, describes four new years for various purposes. The new year for tithes for general crops is the first of Tishrei (the holiday of Rosh Hashanah), for animal tithes the first of Elul, and for the produce of trees the fifteenth of Shevat (the holiday of Tu Bishvat). The Talmud and later commentaries reflect a substantial amount of debate about the start and end of the tithing year for various types of crops in various situations.

The second tithe is a distinct tithing obligation of 10% of the produce after terumah and the first tithe were separated. If any of these tithes were not separated, the produce was known as tevel and forbidden for consumption. The owner of the produce was required to separate tithe, of any kind, after the particular kind of produce was finished in its common preparation for ingathering. Unlike the first tithe, the second tithe was only separated on the first, second, fourth and fifth years of the sabbatical year cycle. The poor tithe was separated on the third and sixth years.

The produce was required to be maintained in a state of purity and eaten in a state of purity in Jerusalem, at any time of the year. If the owner did not desire or was unable to bring the produce to Jerusalem, he was entitled to redeem the produce on a coin of equal value, in addition to adding a fifth to the value. The ability to redeem produce on money results in money which is mikudash (sacred, as earmarked for Temple purposes), while the produce became desanctified and available for ordinary use. The money could only be used for limited categories of use in keeping with its sacred status. Improper spending of the money was forbidden.

After the Second Temple's destruction and the inability to consume fruits of Second Tithe in a state of ritual cleanness, the general practice was to redeem the produce and its sanctity on a coin, and to discard the coin, or else to separate the Second Tithe and to profane its sanctity by having it transferred to a smaller piece of produce of its own kind, such as wine upon wine and grain upon grain. Afterwards, the smaller piece (to which the fruit's Second Tithe sanctity has been transferred) is discarded. In the absence of the Temple and ritual purity, second tithe produce valued at one-hundred denarii can be redeemed on a perutah, and does not require redeeming its full monetary value.