diff --git a/.appveyor.yml b/.appveyor.yml
index b1f25d356fb..27481011927 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -53,5 +53,5 @@ test_script:
         if (!$?) { $host.SetShouldExit(-1) }
       }  # run all examples
   - cd %APPVEYOR_BUILD_FOLDER%\examples\python-guide\notebooks
-  - conda install -q -y -n test-env ipywidgets notebook "tornado=5.1.1"
+  - conda install -q -y -n test-env ipywidgets notebook
   - jupyter nbconvert --ExecutePreprocessor.timeout=180 --to notebook --execute --inplace *.ipynb  # run all notebooks
diff --git a/.ci/test.sh b/.ci/test.sh
index 4c4bef36c91..e5633673fe7 100755
--- a/.ci/test.sh
+++ b/.ci/test.sh
@@ -139,6 +139,6 @@ matplotlib.use\(\"Agg\"\)\
     sed -i'.bak' 's/graph.render(view=True)/graph.render(view=False)/' plot_example.py
     for f in *.py; do python $f || exit -1; done  # run all examples
     cd $BUILD_DIRECTORY/examples/python-guide/notebooks
-    conda install -q -y -n $CONDA_ENV ipywidgets notebook "tornado=5.1.1"
+    conda install -q -y -n $CONDA_ENV ipywidgets notebook
     jupyter nbconvert --ExecutePreprocessor.timeout=180 --to notebook --execute --inplace *.ipynb || exit -1  # run all notebooks
 fi
diff --git a/.ci/test_windows.ps1 b/.ci/test_windows.ps1
index 23963cc6c4d..bae9c25964a 100644
--- a/.ci/test_windows.ps1
+++ b/.ci/test_windows.ps1
@@ -38,6 +38,6 @@ if ($env:TASK -eq "regular") {
     python $file ; Check-Output $?
   }  # run all examples
   cd $env:BUILD_SOURCESDIRECTORY/examples/python-guide/notebooks
-  conda install -q -y -n $env:CONDA_ENV ipywidgets notebook "tornado=5.1.1"
+  conda install -q -y -n $env:CONDA_ENV ipywidgets notebook
   jupyter nbconvert --ExecutePreprocessor.timeout=180 --to notebook --execute --inplace *.ipynb ; Check-Output $?  # run all notebooks
 }