* Euro backs down at $1.21 as profits taken on run-up * Euro faces waves of resistance in $1.2135-75 band * Aussie slips a China data as expected, profits booked

TOKYO, June 11 (Reuters) - The euro ran into headwinds above $1.21 on Friday, as profit-booking set in when it failed to push through hefty resistance, and investors took a lack of surprises in Chinese data to book gains in the Aussie dollar.

The euro, which rose on Thursday for a third straight day, stalled at important resistance in the $1.2135-55 area, with a mixture of sellers and stop-loss buy orders expected above there.

Traders said profit-taking emerged after the euro rallied 1.3 percent on Thursday when higher-yielding currencies such as the Aussie also climbed and share markets rose, adding that the market was cautious the short-covering rally may not last long before the single currency resumed its downward trend.

The run is a little bit exhausted. On the upside the real cap on this is $1.2217 but it's struggling around the $1.2150 level, said Mitul Kotecha, global head of FX strategy at Credit Agricole CIB in Hong Kong.

The euro climbed as far as $1.2149 before slipping back to just above $1.2100. It was last above $1.22 on June 4, before tumbling to a four-year low at $1.2176.

It has a host of chart points in this area, including $1.2135, which is roughly a 50 percent retracement of its 2000-2008 rally. Resistance from former support in May sits at $1.2150-55.

It has shed 1.5 percent this month and nearly 16 percent this year, driven ever lower by fiscal concerns in the euro zone, but it got a lift on Thursday when strong demand for Spanish bonds eased concern about the country's ability to finance its debt.

A spike in Chinese exports also boosted confidence on global growth and investors breathed a sigh of relief after European Central Bank President Jean-Claude Trichet said three-month emergency loans to banks would continue until September.

A trader said the ECB's move had encouraged some in the market to be build positions for the next quarter by buying higher yielding currencies such as the Australian dollar.

But after another round of Chinese data on Friday was in line with leaks and forecasts, Nobuhiko Akai, senior manager of forex trading group at Bank of Tokyo-Mitsubishi UFJ, said those who bought the Aussie quickly took profits.

The latest rebound buying in the euro is still driven by short-covering. Unless it goes back to around $1.25, market sentiment will not change drastically, Akai said.

The euro retreated below 111.00 yen after pushing back above that level for the first time in a week, while the dollar rose 0.2 percent to 91.50 yen.

Higher yielding and commodity-linked currencies forged big gains against the dollar and the yen on Thursday, helped by Chinese trade numbers.

The dollar index, which hit at 15-month high 88.708 on Monday, has since retreated below 88.0 and was flat on the day at 87.176 .DXY.

But the Aussie, which jumped 2.7 percent in the previous session, failed to maintain a move above $0.8500, faltering at resistance at $0.8510 and retreated to $0.8465.

If it can move higher, it faces more resistance at $0.8550 and then about $0.8570, which is a 38.2 percent retracement of its drop from an April high near $0.94 and a May low at $0.8066.

We are seeing a bit of a cautious move, a gradual step back in but we're a long way from a big rush back in, Kotecha said. (Additional reporting by Satomi Noguchi and Hideyuki Sano in Tokyo, and Reuters FX analysts Rick Lloyd in Singapore and Krishna Kumar in Sydney; Editing by Edwina Gibbs)