I gave him a box, inside the box was a gift.

[theol]

I gave him a box, inside the box was a gift.

Is a comma a good way to connect these two sentence? If not, how can I make changes of it?

 

[Skrej]

I gave him a box, inside the box was a gift.

Is a comma a good way to connect these two sentence? If not, how can I make changes of to it?

No, a comma will not work because it creates a comma splice. Either use a period and start a new sentence, or use a semi-colon. A third option is to use a coordinating conjunction with the comma. The final option would be a subordinating conjunction, although you have rather limited possible choices with these two particular clauses.

 

[Tarheel]

@theol You can keep the comma if you do this:

I gave him a box, and inside the box was a gift.

 

[jutfrank]

You can avoid repetition of box by forming a relative clause:

I gave him a box, inside which was a gift.
I gave him a box, which had a gift inside.

Another option is to use with:

I gave him a box with a gift inside.

 

[Rover_KE]

I can't help envisioning a mother saying to her daughter 'Pandora, whatever you do, don't open that box your Uncle Zeus gave you.

I said 'DON'T OPEN THAT BO ... AWW CRA ...

 

[Skrej]

I can't help envisioning a mother saying to her daughter 'Pandora, whatever you do, don't open that box your Uncle Zeus gave you.

I said 'DON'T OPEN THAT BO ... AWW CRA ...

Sounds like a Neil Gaiman short story in the making.