Abstract: Contract Law in China defines the legal nature of commercial ads as offer invitation. Two requirements are to be filled for the tenability of the definition. One is that the ad should indeed show the content of will that the ad master “hopes that others will express their intention to propose an offer to him”; the other is that if the ad, master keeps up the will mentioned, what he means will surely solicit “offer” to him not whatever else. But analysis shows that the two requirements are not fulfilled. It also shows that the commercial ad master’s content of will can be divided into the main part of the positive will, i.e.“to invite” offer invitation and the secondary part of the negative will,i.e. to invite“offer invitation”. Hence one can see that the legal nature of commercial ads is relatively complicated. And the legal nature defined by Contract Law is by no means accurate.

Key words: Commercialads, legalnature, offerinvitation