Trump told thousands of his supporters that he supported the second amendment of the Constitution on gun rights, Xinhua news agency reported.
"Nobody will protect your Second Amendment like Donald Trump," he said, adding that the worst shooting massacre in US history could have been prevented earlier this week if patrons of the nightclub involved in Orlando had been armed.
"If some of those wonderful people had guns strapped to their waist or strapped to their ankle and this son of a (expletive) comes out and starts shooting, and one of the people happened to have it and goes 'boom, boom,' that would have been a beautiful, beautiful sight," he said. "So don't let them take their guns away. We're going to save your Second Amendment."
Trump said that his presumptive Democrat opponent, former Secretary of State Hillary Clinton, would destroy the second amendment granting Americans the right to bear arms.
On his immigration policy, Trump reiterated his plan to protect the US border with neighbouring Mexico by building a wall.
"It's going to be as beautiful as a wall can be. I have to make it beautiful because maybe one day they'll name it the Trump Wall," he said.
Trump arrived early Friday evening at the Woodlands Waterway Marriott Hotel and Convention Centre just north of Houston.
Security was on high alert as peaceful groups of protesters displayed anti-Trump slogans outside the centre and downtown, and one man armed with a gun was arrested prior to Trump's arrival.
Earlier that afternoon, Trump attended a private fundraiser in Houston's wealthiest neighbourhood, where about 200 guests paid from $5,400 to $250,000 for entry and personally meet the hotel, casino and golf course entrepreneur and former TV game show host, who is now heading the Republican presidential nomination.
Houston is Trump's final stop of a two-day Texas tour that included a Dallas fundraiser and rally before a crowd of 3,500 people next Thursday.
This is Trump's first campaign to Texas since entering the Republican race one year ago.