The 1988 California State Senate elections were held on November 8 in the twenty odd-numbered Senate districts. There was no change to the representation of the Democratic and Republican parties.

The 1990 California State Senate elections were held on November 6, 1990. Senate seats of even-numbered districts were up for election. Senate terms are staggered so that half the membership is elected every two years. Senators serve four-year terms and are limited to two terms. The Democratic party won 15 seats, gaining a seat from the Republicans. The Republicans won 4 seats, and Independent Quentin L. Kopp was reelected.