Xavi, Daniel Alves and Lionel Messi scored to round off a positive week for the champions, in which coach Pep Guardiola ended speculation over his future by agreeing to a one-year contract extension.
Barca have 49 points from 19 games.
"It's no bad thing to finish the first half of the season unbeaten but it is little more than an anecdote. There are still many games to play," Guardiola told reporters.
As has happened in recent games, Barca were on the back foot and struggling under some intense pressure from their hosts before they broke away to score in the 20th minute.
A sweeping counter-attack from deep in their own half ended with Alves crossing for Xavi to volley home from inside the area.
Almost immediately, Alves was galloping down the flank again and this time his looping cross from wide on the right drifted over Justo Villar and into the net.
Saves from Victor Valdes kept Valladolid at bay and in the 56th minute Zlatan Ibrahimovic set up Messi for the third, and the Argentine's 15th of the season, to end the match as a contest.
SERIOUS INJURY
In the late game, Deportivo La Coruna overcame Athletic Bilbao 3-1 at home to climb to fourth on 34 points, but the game was overshadowed by the serious injury suffered by Depor defender Filipe.
The Brazilian scored the first goal after 49 minutes but broke his right leg near the ankle as he collided with the visiting goalkeeper, and was rushed to hospital.
Juca and Pablo Alvarez made sure of the win, with Depor defender Diego Colotto scoring in his own net for Bilbao's goal.
Earlier, Sevilla beat Almeria 1-0 with an Alvaro Negredo goal after some quick thinking on a waterlogged pitch at the Sanchez Pizjuan, to go sixth with 33 points.
Heavy rain during the day made life difficult for both sides at first, with the ball regularly being held up in puddles, and forced an error from the visitors after 10 minutes.
Santiago Acasiete's backpass to his goalkeeper ran up short in the area and Renato nipped in and squared for Negredo to score in the empty net.
But Sevilla had to endure a nervy 80 minutes before securing the points to end a run of four straight league defeats.
