diff --git a/taskflow/engines/worker_based/worker.py b/taskflow/engines/worker_based/worker.py
index 609339de..f6fe608f 100644
--- a/taskflow/engines/worker_based/worker.py
+++ b/taskflow/engines/worker_based/worker.py
@@ -71,9 +71,14 @@ class Worker(object):
     def __init__(self, exchange, topic, tasks, executor=None, **kwargs):
         self._topic = topic
         self._executor = executor
-        self._threads_count = kwargs.pop('threads_count',
-                                         tu.get_optimal_thread_count())
+        self._threads_count = -1
         if self._executor is None:
+            if 'threads_count' in kwargs:
+                self._threads_count = int(kwargs.pop('threads_count'))
+                if self._threads_count <= 0:
+                    raise ValueError("threads_count provided must be > 0")
+            else:
+                self._threads_count = tu.get_optimal_thread_count()
             self._executor = futures.ThreadPoolExecutor(self._threads_count)
         self._endpoints = self._derive_endpoints(tasks)
         self._server = server.Server(topic, exchange, self._executor,
@@ -114,11 +119,15 @@ class Worker(object):
 
     def run(self):
         """Run worker."""
-        LOG.info("Starting the '%s' topic worker in %s threads." %
-                 (self._topic, self._threads_count))
+        if self._threads_count != -1:
+            LOG.info("Starting the '%s' topic worker in %s threads.",
+                     self._topic, self._threads_count)
+        else:
+            LOG.info("Starting the '%s' topic worker using a %s.", self._topic,
+                     self._executor)
         LOG.info("Tasks list:")
         for endpoint in self._endpoints:
-            LOG.info("|-- %s" % endpoint)
+            LOG.info("|-- %s", endpoint)
         self._server.start()
 
     def wait(self):