The Briton returned to the cockpit of the W04 at Barcelona for his first outing with Mercedes at the Spanish Grand Prix venue.
Hamilton was the busiest man on track today, completing 121 laps on his way to the fourth fastest time of the day.
The former world champion said his team is not looking at what its rivals are doing, but he felt the car was stronger than in the first test.
"We're just focusing on ourselves and working on our programme for the first race, and it's going in the right direction," said Hamilton.
"At the last test the tyres didn't behave so well because the car wasn't behaving so well. Here it's much better."
Hamilton was non-committal about Mercedes's goals for the start of the season, but he said he was delighted with how the team was working to move forward.
"It's so encouraging to see the amount of work that's going in and to see the atmosphere there and see how determined everyone is," he said.
"I've got a great group of guys behind me. I'm sure they've been working hard over the years, but I've only just arrived and immediately I see just a fantastic determination and effort going in. I hope it all pays off."