The August 15-16 poll found that 52 per cent of Republicans were not happy with Trump as the party nominee, while 46 per cent were pleased, Xinhua news agency reported on Sunday.
In comparison, Democrats were more satisfied with Hillary Clinton as their nominee, with 56 per cent saying they were pleased while 42 per cent wish someone else were nominated.
Though more than half of Republicans wished someone other than Trump were their party's nominee, only less than a third held an unfavorable opinion of Trump.
Similarly, while more than four in 10 Democrats say they wished someone other than Clinton were their party's nominee, only about two in 10 view Clinton unfavourably, Gallup noted.
Trump recently shook up his staff in an effort to regain his campaign's momentum, but his choice of the chairman of the highly conservative Breitbart website to be his campaign chief doesn't signal that Trump was focused on reaching out to expand his appeal to more centrist or moderate voters, Gallup said.
Clinton faces the continuing challenge of particularly low satisfaction among younger Democrats, who may still be thinking about her former rival Bernie Sanders, who saw strong support among younger voters.
According to Gallup, only 38 per cent of Democrats and Democratic leaders between the ages of 18 and 39 were satisfied with Clinton, compared with 67 per cent of those 40 and older.
Additionally, 47 per cent of non-Hispanic white Democrats were satisfied with Clinton as their party's nominee, compared with 67 per cent of non-white Democrats.
This reinforces the idea that Clinton would depend heavily on support from black, Hispanic and other non-white Democrats in her effort to get a winning coalition to the polls in November, Gallup said.