I think Thai is more difficult than Chinese, because I am Chinese,haha. Actually I think Chinese and Thai     does share something in common. Both have tones and different words to mean the same thing. For example 'YOU' in Chinese "ni" and "nin",the latter is more polite and in Thai “te” and “kun”

As I have been to Thailand and know some Thai. There is one significant difference between them. Thai  usually put adj before the noun but Chinese does not. For example "old friend"  "lao(old

) pengyou(friend)" but Thai "pern(friend) gao(old)".

The grammar of both are similar but not with the tone and the pronunciation. We Thai people pronounce things clearer. The order of the sentences are slightly different but it is easier to learn Thai than Chinese although there are more resources for learning Chinese.

Dear Shaun,

Thai is very similar to Chinese. In fact, the similarity is strong enough for the Thai language to adopt Chinese writing system (which may actually happened in the past). Idioms and expressions are pretty similar too. If you say in chinese "qu qu lai lai" that woul be "pai pai ma ma" in Thai and it means the same thing (i.e. "comes and goes"). It is pretty easy for Thais to learn to speak Chinese, although learning to write the character will take time. But Thai language is certainly closer to Chinese than Japanese (whose adoption of Chinese characters was tragic). Thai and Chinese don't have tenses, the verbs do not conjugate. Besides, Thai has adopted many Chinese words. 

But in a higher level of use, Thai adopts terms from Sanscrit and Pali which belong to Indo-European family. Most formal words or difficult terms will have roots in sanscrit/pali; it's just like the way technical terms in English have roots in Latin or Greek. Thai writing system is actually designed to assist importation of these Sanscrit/pali terms. That's why there are many redundant alphabets.    

Hi Shaun

I've spent 3 years learning Chinese and this year I've started learning Thai. It's true that there are lots of similarities with the grammar. I would say it's about 60% the same. Thai also uses measure words like mandarin but it's works slightly different. The tones are similar apart from the high tone in Thai which is very different. Thai is easier to learn than chinese. Athought there are a lot more resources to learn Chinese. It's harder to find people to practice thai with. But yes the Grammar is similar. I hope that helps.

We have five tones in Thai but in Mandarin, they have four tones.

I find Mandarin more difficult than Thai, especially the traditional one. 

As for grammar, it is quite similar.