diff --git a/torch/optim/adadelta.py b/torch/optim/adadelta.py
index ae9286a5cb2f..e090f62012b4 100644
--- a/torch/optim/adadelta.py
+++ b/torch/optim/adadelta.py
@@ -1,5 +1,6 @@
 import torch
 
+from . import functional as F
 from .optimizer import Optimizer
 
 
@@ -49,32 +50,41 @@ def step(self, closure=None):
                 loss = closure()
 
         for group in self.param_groups:
+            params_with_grad = []
+            grads = []
+            square_avgs = []
+            acc_deltas = []
+
             for p in group['params']:
                 if p.grad is None:
                     continue
-                grad = p.grad
-                if grad.is_sparse:
+                params_with_grad.append(p)
+                if p.grad.is_sparse:
                     raise RuntimeError('Adadelta does not support sparse gradients')
+                grads.append(p.grad)
+
                 state = self.state[p]
 
-                # State initialization
+                # Lazy state initialization
                 if len(state) == 0:
                     state['step'] = 0
                     state['square_avg'] = torch.zeros_like(p, memory_format=torch.preserve_format)
                     state['acc_delta'] = torch.zeros_like(p, memory_format=torch.preserve_format)
 
-                square_avg, acc_delta = state['square_avg'], state['acc_delta']
-                rho, eps = group['rho'], group['eps']
+                square_avgs.append(state['square_avg'])
+                acc_deltas.append(state['acc_delta'])
 
-                state['step'] += 1
+                lr, rho, eps, weight_decay = group['lr'], group['rho'], group['eps'], group['weight_decay']
 
-                if group['weight_decay'] != 0:
-                    grad = grad.add(p, alpha=group['weight_decay'])
+                state['step'] += 1
 
-                square_avg.mul_(rho).addcmul_(grad, grad, value=1 - rho)
-                std = square_avg.add(eps).sqrt_()
-                delta = acc_delta.add(eps).sqrt_().div_(std).mul_(grad)
-                p.add_(delta, alpha=-group['lr'])
-                acc_delta.mul_(rho).addcmul_(delta, delta, value=1 - rho)
+            F.adadelta(params_with_grad,
+                       grads,
+                       square_avgs,
+                       acc_deltas,
+                       lr,
+                       rho,
+                       eps,
+                       weight_decay)
 
         return loss
diff --git a/torch/optim/functional.py b/torch/optim/functional.py
index dd6cd3ca7b3c..725dead7e37a 100644
--- a/torch/optim/functional.py
+++ b/torch/optim/functional.py
@@ -132,3 +132,27 @@ def sgd(params: List[Tensor],
                 d_p = buf
 
         param.add_(d_p, alpha=-lr)
+
+
+def adadelta(params: List[Tensor],
+             grads: List[Tensor],
+             square_avgs: List[Tensor],
+             acc_deltas: List[Tensor],
+             lr: float,
+             rho: float,
+             eps: float,
+             weight_decay: float):
+    r"""Functional API that performs Adadelta algorithm computation.
+
+    See :class:`~torch.optim.Adadelta` for details.
+    """
+
+    for (param, grad, square_avg, acc_delta) in zip(params, grads, square_avgs, acc_deltas):
+        if weight_decay != 0:
+            grad = grad.add(param, alpha=weight_decay)
+
+        square_avg.mul_(rho).addcmul_(grad, grad, value=1 - rho)
+        std = square_avg.add(eps).sqrt_()
+        delta = acc_delta.add(eps).sqrt_().div_(std).mul_(grad)
+        param.add_(delta, alpha=-lr)
+        acc_delta.mul_(rho).addcmul_(delta, delta, value=1 - rho)