Chilean winger Sanchez has been a standout performer for Arsenal this season, scoring 18 goals in all competitions since his ??30m move from Barcelona in the summer.
The South Americans come up against each other when Arsenal visit Manchester City on Super Sunday, live on Sports 1 HD, and Pellegrini admits he has been impressed by Sanchez???s goalscoring heroics.
He said: “I think Alexis is a very good player, he is having a very good season in England.
“It is not easy for a player in his first season here to score so many goals, (but) Alexis is repeating what he did in the last two seasons at Barcelona and scoring a lot of goals.
“I am very happy for him because he is a young player and a very enthusiastic player and improving. The football fans in Chile are very happy for him and for the country.”
Sanchez was sought by a number of clubs last year including Liverpool, but Pellegrini claims adding the 26-year-old to City???s ranks over the summer was not a viable option.
He said: “It was not easy, he was a very expensive player in that moment.
“In the moment Barcelona sold him to Arsenal we were not searching for one striker because we had, in that moment, (Stevan) Jovetic, Aguero, (Alvaro) Negredo and (Edin) Dzeko, but I am sure Alexis can play everywhere.”
Pellegrini thinks Sunday???s clash will be an entertaining affair but does not expect a repeat of the 6-3 scoreline City beat Arsenal by in the corresponding fixture last season.
He said: ???Both teams play very attractive football and they have very good players, so we hope we will see a very good match.
“It is a very important game. Arsenal are a strong team. I always say maybe they are not top of the table but they always have high targets for every season. I hope we will have a very good game and add three more points.
“It is difficult to score six and three goals again, but I think for fans it will be a very attractive game. I hope we can score the same amount of goals and Arsenal have more problems to score three goals.”
City???s draw at Everton last weekend saw Pellegrini???s side slip two points behind Premier league leaders Chelsea but the Chilean is confident his team can still go on and win the title.
He added: “We have to play 17 games more and that is 51 points – 51 and 47 are 98, so we can drop points and win the title. I am sure that all the teams will drop points between now and the end of the year.
“The less you drop the better but it is important to try to recover to the top of the table in this month.”