diff --git a/moto/ec2/models/instances.py b/moto/ec2/models/instances.py
index 530d8097d..8ae642c44 100644
--- a/moto/ec2/models/instances.py
+++ b/moto/ec2/models/instances.py
@@ -111,6 +111,7 @@ class Instance(TaggedEC2Resource, BotoInstance, CloudFormationModel):
         self.instance_type: str = kwargs.get("instance_type", "m1.small")
         self.region_name = kwargs.get("region_name", "us-east-1")
         placement = kwargs.get("placement", None)
+        self.placement_hostid = kwargs.get("placement_hostid")
         self.subnet_id = kwargs.get("subnet_id")
         if not self.subnet_id:
             self.subnet_id = next(
diff --git a/moto/ec2/responses/instances.py b/moto/ec2/responses/instances.py
index c1ec8fc92..c3bbf45ee 100644
--- a/moto/ec2/responses/instances.py
+++ b/moto/ec2/responses/instances.py
@@ -61,6 +61,7 @@ class InstanceResponse(EC2BaseResponse):
             "instance_type": self._get_param("InstanceType", if_none="m1.small"),
             "is_instance_type_default": not self._get_param("InstanceType"),
             "placement": self._get_param("Placement.AvailabilityZone"),
+            "placement_hostid": self._get_param("Placement.HostId"),
             "region_name": self.region,
             "subnet_id": self._get_param("SubnetId"),
             "owner_id": owner_id,
@@ -470,6 +471,7 @@ EC2_RUN_INSTANCES = """<RunInstancesResponse xmlns="http://ec2.amazonaws.com/doc
           <instanceLifecycle>{{ instance.lifecycle }}</instanceLifecycle>
           {% endif %}
           <placement>
+            {% if instance.placement_hostid %}<hostId>{{ instance.placement_hostid }}</hostId>{% endif %}
             <availabilityZone>{{ instance.placement}}</availabilityZone>
             <groupName/>
             <tenancy>default</tenancy>
@@ -627,6 +629,7 @@ EC2_DESCRIBE_INSTANCES = """<DescribeInstancesResponse xmlns="http://ec2.amazona
                     <instanceLifecycle>{{ instance.lifecycle }}</instanceLifecycle>
                     {% endif %}
                     <placement>
+                      {% if instance.placement_hostid %}<hostId>{{ instance.placement_hostid }}</hostId>{% endif %}
                       <availabilityZone>{{ instance.placement }}</availabilityZone>
                       <groupName/>
                       <tenancy>default</tenancy>
diff --git a/tests/test_ec2/test_instances.py b/tests/test_ec2/test_instances.py
index ca07b812f..7122f75d7 100644
--- a/tests/test_ec2/test_instances.py
+++ b/tests/test_ec2/test_instances.py
@@ -1326,6 +1326,23 @@ def test_run_instance_with_specified_private_ipv4():
     assert instance["PrivateIpAddress"] == "192.168.42.5"
 
 
+@mock_ec2
+def test_run_instance_with_placement():
+    client = boto3.client("ec2", region_name="eu-central-1")
+    host_id = "h-asdfasdfasdf"
+
+    instance = client.run_instances(
+        ImageId=EXAMPLE_AMI_ID, MaxCount=1, MinCount=1, Placement={"HostId": host_id}
+    )["Instances"][0]
+    instance_id = instance["InstanceId"]
+    assert instance["Placement"]["HostId"] == host_id
+
+    resp = client.describe_instances(InstanceIds=[instance_id])["Reservations"][0][
+        "Instances"
+    ][0]
+    assert resp["Placement"]["HostId"] == host_id
+
+
 @mock_ec2
 def test_run_instance_mapped_public_ipv4():
     client = boto3.client("ec2", region_name="eu-central-1")