Mesh.subMeshCount

public int subMeshCount ;

Description

The number of sub-Meshes. Every Material has a separate triangle list.

See Also: GetTriangles, SetTriangles.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Start() {
        Mesh mesh = GetComponent<MeshFilter>().mesh;
        Debug.Log("Submeshes: " + mesh.subMeshCount);
    }
}