diff --git a/cli/src/main/java/org/onlab/onos/cli/MastersListCommand.java b/cli/src/main/java/org/onlab/onos/cli/MastersListCommand.java
index 0f7857f..fff4955 100644
--- a/cli/src/main/java/org/onlab/onos/cli/MastersListCommand.java
+++ b/cli/src/main/java/org/onlab/onos/cli/MastersListCommand.java
@@ -1,7 +1,9 @@
 package org.onlab.onos.cli;
 
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ArrayNode;
 import com.google.common.collect.Lists;
-
 import org.apache.karaf.shell.commands.Command;
 import org.onlab.onos.cluster.ClusterService;
 import org.onlab.onos.cluster.ControllerNode;
@@ -26,15 +28,50 @@
         MastershipService mastershipService = get(MastershipService.class);
         List<ControllerNode> nodes = newArrayList(service.getNodes());
         Collections.sort(nodes, Comparators.NODE_COMPARATOR);
+
+        if (outputJson()) {
+            print("%s", json(service, mastershipService, nodes));
+        } else {
+            for (ControllerNode node : nodes) {
+                List<DeviceId> ids = Lists.newArrayList(mastershipService.getDevicesOf(node.id()));
+                Collections.sort(ids, Comparators.ELEMENT_ID_COMPARATOR);
+                print("%s: %d devices", node.id(), ids.size());
+                for (DeviceId deviceId : ids) {
+                    print("  %s", deviceId);
+                }
+            }
+        }
+    }
+
+    // Produces JSON structure.
+    private JsonNode json(ClusterService service, MastershipService mastershipService,
+                          List<ControllerNode> nodes) {
+        ObjectMapper mapper = new ObjectMapper();
+        ArrayNode result = mapper.createArrayNode();
         ControllerNode self = service.getLocalNode();
         for (ControllerNode node : nodes) {
             List<DeviceId> ids = Lists.newArrayList(mastershipService.getDevicesOf(node.id()));
-            Collections.sort(ids, Comparators.ELEMENT_ID_COMPARATOR);
-            print("%s: %d devices", node.id(), ids.size());
-            for (DeviceId deviceId : ids) {
-                print("  %s", deviceId);
-            }
+            result.add(mapper.createObjectNode()
+                               .put("id", node.id().toString())
+                               .put("size", ids.size())
+                               .set("devices", json(mapper, ids)));
         }
+        return result;
+    }
+
+    /**
+     * Produces a JSON array containing the specified device identifiers.
+     *
+     * @param mapper object mapper
+     * @param ids    collection of device identifiers
+     * @return JSON array
+     */
+    public static JsonNode json(ObjectMapper mapper, Iterable<DeviceId> ids) {
+        ArrayNode result = mapper.createArrayNode();
+        for (DeviceId deviceId : ids) {
+            result.add(deviceId.toString());
+        }
+        return result;
     }
 
 }