Elections to the Massachusetts Senate were held during 1787 to elect 40 State Senators. Candidates were elected at the county level, with some counties electing multiple Senators.

For election, a candidate needed the support of a majority of those voting. If a seat remained vacant because no candidate received such majority, the Massachusetts General Court was empowered to fill it by a majority vote of its members.

The primary issue in this race was the ongoing ratification of the United States Constitution by a separate ratifying convention; the reaction divided the state (and nation) between Federalists and Anti-Federalists, though the factions did not appear as strictly formal political parties until 1789.

The elections were also held during the midst of Shays' Rebellion, an armed uprising in Western Massachusetts against the national government, formed in opposition to the ongoing debt crisis.

The apportionment of seats by population was as follows:

• Barnstable County: 1
• Berkshire County: 2
• Bristol County: 3
• Cumberland County: 1
• Dukes and Nantucket Counties: 1
• Essex County: 6
• Hampshire County: 4
• Lincoln County: 1
• Middlesex County: 5
• Plymouth County: 3
• Suffolk County: 6
• Worcester County: 5
• York County: 2