I read it in an article and I don't understand the meaning of it.
"not without some merit".
From the context I guess the meaning is: there is some sense in it.
However I don't find in the dictionary (vocabulary.com or thefreedictionary.com) an explanation that apt my understanding.
Nor I've found an expression with "merit" that can explain it.
The article is here:
http://www.theguardian.com/technology/2016/jan/03/hi-tech-silicon-valley-cult-populism
Best Answer
From your linked article:
There's more here to be confused by than the expression, "not without some merit".
The expression is used parenthetically. So you should be able to remove it from the sentence completely and decode its main meanings: the mayor took the taxi industry's side. Uber is good.
Adding "not without some merit" shows that the author agrees with Uber, at least in part.
"Not without" is a double negative that is NOT used here for emphasis. It means, "It would be wrong to say this is completely false". That's not as strong as saying "it's completely true".