Michigan State Highway 43, or M-43, is a highway in southwestern and central Michigan from South Haven, junction Interstate 196 to Webberville, junctions Interstate 96 and Michigan State HIghway 52 .

Although it goes through Kalamazoo and Lansing, it is little used as a through route between those two large cities because it is less direct and fast than Interstate 94 and Interstate 69.

Effectively, M-43 is several different highways, generally from west to east:

1. Between South Haven and Kalamazoo, a nearly east-west surface highway. Starting from downtown South Haven it takes an eastward course and crosses over Interstate 196-U.S. Highway 31, passing through Bangor. As it approaches Kalamazoo it becomes divided surface road, has an interchange with the U.S. Highway 131 freeway, and leads to downtown Kalamazoo.
2. Between Kalamazoo and Hastings, a route that angles slightly north of east toward Richland, Michigan, meets Michigan State Highway 89, and turns sharply northward toward Hastings, where it meets Michigan State Highway 37.
3. Between Hastings and downtown Lansing, a largely east-west route through Woodbury (junctions with Michigan State Highway 50 and Michigan State Highway 66) and Grand Ledge, where it meets Michigan State Highway 100. On the west side of greater Lansing it has an intersection with Interstate 69 and Interstate 96 and becomes Business Loop 69 to downtown Lansing, where it ended at its intersection with the old U.S. Highway 16 before the 1960s, when US 16 was diverted to the new Interstate 96 freeway before being decommissioned throughout Michigan.
4. Finally, the section of old US 16, the Grand River Road, through East Lansing, intersecting the U.S. Highway 127 freeway and Michigan State University east-south-eastward through Okemos and Williamston to its eastern terminus near Webberville.

The sections of M-43 through greater Lansing and especially near Michigan State University is often extremely slow due to congestion resulting from commercial and commuter traffic. None of M-43 is expressway, although it has numerous interchanges with freeways which offer more direct routes for many motorists who have destinations along its route.