Langer, who played with Strauss at English county side Middlesex and still keeps in contact, said while he was delighted for his friend's explosive start to his international career, his achievements were a concern for Australia.
"It makes me nervous when they've got guys like him in the side," Langer said here on Thursday.
"He could always get to 30 and 40 so easily because his technique and everything was right; now he's got that hunger to make runs.
"He's a very good player in their side because ... he's a very strong character."
South African-born Strauss, 27, has taken English cricket by storm since scoring a century on his Test debut against New Zealand at Lord's in May.
He made another hundred against the West Indies in July and then became the first player to score debut hundreds against three different opponents when he struck 126 against South Africa in Port Elizabeth last week.
His first eight Tests produced eight wins for England and his ninth -- the second Test against South Africa in Durban -- has brought a fourth century.
Strauss has scored 971 runs in 18 innings and should become the fourth-fastest England player to reach 1,000 runs after greats Herbert Sutcliffe (12 innings), Len Hutton (16) and Walter Hammond (18).
The left-handed Strauss made a huge impression on Langer during their three seasons at Middlesex.
"A lot of guys talk about wanting to play for England; he didn't really talk about it too much but he showed that he wanted to play," Langer said.
"I was always impressed by the way he went about his business. You watch guys play touch football or play soccer in the lead-up (to games) and you can tell something about the person.
"He was always like a little bulldog, really competitive in touch footy or playing football -- always competitive."
Langer compared a showdown against England containing Strauss and opening partner Marcus Trescothick, captain Michael Vaughan, all-rounder Andrew Flintoff and fast bowler Stephen Harmison to the challenge of beating India at home.
"It will be a lot of pressure on this time," he said.
"There always is with Ashes tours because both countries are cricket countries and have got big egos and they want to win the Ashes, so it will be a great contest."