The two planets in our solar system that have similar mass and size are Earth and Venus.

Here's a comparison:

* Earth:

* Mass: 5.972 × 10^24 kg

* Diameter: 12,742 km

* Venus:

* Mass: 4.867 × 10^24 kg

* Diameter: 12,104 km

As you can see, Venus is slightly smaller and less massive than Earth, but the difference is relatively minor compared to other planets in our solar system.