Gather all ingredients.
Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch baking dish.
To make the cake: Stir together flour, sugar, baking soda, and salt in a large bowl.
Stir in eggs and sour cream until smooth, then fold in rhubarb.
Pour into the prepared dish and spread evenly.
To make the streusel: Stir together sugar and butter in a medium bowl until smooth. Stir in flour until mixture is crumbly.
Sprinkle mixture on top of cake, then dust lightly with cinnamon.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 45 minutes.
Serve and enjoy!